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The video cassette recorder is a wonderful example of extremely complex precision technology that has been made affordable through mass production. In general, it is usually quite reliable. Treat a modern VCR with a bit of respect and it will provide trouble free service for a long time. Unlike a TV where the power circuits take their toll on circuit components, the electronics in VCR are generally quite reliable and rarely fail. Most VCR problems are mechanical - dirt and dust in the tape path, deteriorated rubber parts, dried lubrication, wear of precision parts including the spinning video heads, and abuse caused by rocks, toys, and peanut butter and jelly sandwiches.
Note: Links to all the diagrams and photographs referenced from this document can be found in Sam's VCR FAQ Files.
Even if you are a technoklutz who lets your kids change the light bulbs in your house and would never consider tackling any actual repair or internal maintenance of your VCR, some basic awareness of the principles of video recording and the likely causes for common problems will enable you to intelligently deal with the service technician. You will be more likely to be able to recognize if you are being taken for a ride by a dishonest or just plain incompetent repair center. For example, did you know that one of the most dreaded of problems - the tape eating VCR - can often be remedied by a thorough cleaning and a 50 cent rubber tire?
This document will provide you with the knowledge to deal with over 85% of the problems you are likely to encounter with your VCRs. It will enable you to diagnose problems and in most cases, correct them as well. First and foremost are the techniques for cleaning of the tape path and replacement of rubber parts like belts, tires, and the pinch roller - the solution to many common problems with VCRs. With minor exceptions, specific manufacturers and models will not be covered as there are so many variations that such a treatment would require a huge and very detailed text. Rather, the most common problems will be addressed and enough basic principles of operation will be provided to enable you to narrow the problem down and likely determine a course of action for repair. In many cases, you will be able to do what is required for a fraction of the cost that would be charged by a repair center.
Should you still not be able to find a solution, you will have learned a great deal and be able to ask appropriate questions and supply relevant information if you decide to post to sci.electronics.repair. It will also be easier to do further research using a repair text such as the ones listed at the end of this document. In any case, you will have the satisfaction of knowing you did as much as you could before taking it in for professional repair. With your new-found knowledge, you will have the upper hand and will not easily be snowed by a dishonest or incompetent technician.
If you need to send or take the VCR to a service center, even a simple repair could easily exceed half the cost of a new VCR. Service centers may charge up to $50 or more for providing an initial estimate of repair costs but this will usually be credited toward the total cost of the repair (of course, they may just jack this up to compensate for their bench time).
If you can do the repairs yourself, the equation changes dramatically as your parts costs will be 1/2 to 1/4 of what a professional will charge and of course your time is free. The educational aspects may also be appealing. You will learn a lot in the process. Thus, it may make sense to repair that old clunker so the kids will have their own VCR or you will have a convenient means of copying tapes (legally, of course).
BTW, if you ARE one of those individuals (and there are bucket loads) who doesn't bother (or doesn't know how) to set the clock on your VCR, there is a solution - at least the next time you need to purchase a new VCR. These machines search for a TV station that includes the time code in its transmission format (it is in the vertical blanking interval should you care) and automagically sets the VCR's clock from that information. There - no more flashing 12:00! Many VCRs have this feature nowadays.
Prior to practical video tape recording, the only way to preserve a TV show was to use special equipment that essentially made a film of it off of a video monitor. The quality of such recordings was not very good, editing was difficult, the film needed to be developed so playback was not immediate, and of course, the film could not be erased and reused.
The first successful commercial video tape recorder was introduced around 1956 with the Ampex Quadplex - a $50,000 machine using 2 inch open reel tape and a high speed spinning head with 4 pickups rotating across the tape. This event revolutionized commercial broadcasting. However, this technology was much too complex, cumbersome, and expensive for consumer use and has a number of technological disadvantages as well.
For a consumer video tape recorder to be successful it was felt that the following three major hurdles had to be overcome:
The rotating heads of the Quadplex machine provided the needed tape-head speed to achieve sufficient video bandwidth. However, the transport was much too complex for a consumer machine. Another disadvantage was that since a video frame consists of many adjacent tracks on the tape (16), special effects like stop motion as well as forward and reverse search were not possible without a frame store. While this would not be out of the question today, the cost of such a device in the 1950's would necessitate the consumer taking out a second mortgage to pay for it. Finally, the 2 inch wide format required too much tape for achieving a cost effective 1 hour program time and made the design of a manageable cassette an impossibility. A separate room would be needed to house a modest size video tape library!
Helical scan overcomes most of these problems. See: Helical Scan Video Head Assembly. Rather than scanning across the tape, the tape is wrapped a bit over 180 degrees around a rotating drum at a slight angle. Thus, successive tracks are written diagonally across the tape and can thus be much longer than the width of the tape as in the Quadplex. The tape, therefore can be rather narrow. The first helical scan tapes used a 1 inch format but narrower tape soon followed. The most common formats today are forms of VHS (and Beta) at 1/2", and 8 mm (mostly used for portable applications in camcorders and data storage.) 4 mm tape is used for high quality audio (DAT) as well as data storage.
Each VHS track corresponds to 1 field of the interlaced video format. See: VHS Tape Format. Generally, two heads opposite each other on the rotating head drum are used. One rotation of the drum corresponds to a complete video frame with heads designated A and B for the even and odd fields respectively. What this also provides is the ability to easily implement a variety of special effects including freeze frame, and fully variable speed forward and reverse motion with a recognizable and in many cases, quite clear picture. With relatively minor restriction, this becomes as simple as moving the tape forward or backward or keeping it stationary.
For a not too terrible ASCII diagram and additional discussion, also see the section: VHS physical tape format
(Camcorders and other compact systems may use 2 pairs of identical heads where the opposing pairs are separated by 270 instead of 180 degrees. Physically, there are 4 heads spaced equally around a drum 2/3rds the size of the normal VHS drum. However, successive head in the sequence is 270 degrees apart. In other woeds, if the heads are numbered 1,2,3,4, they are used in the order: 1,4,3,2,1,4... This permits the use of a smaller, lighter video drum but the recorded format is identical.)
The A and B heads are not identical either. Their azimuth angle differs being +6 degrees for one and -6 degrees for the other. See: VHS Video Head Pair Azimuth Angles. This is one of several techniques used to minimize crosstalk between adjacent tracks. Azimuth angle is how far the head gap is from being perfectly perpendicular to the direction of tape-tape motion. For example, a head with an azimuth such as / will ignore most of the information recorded with an azimuth of \.
Note that the head gap - the distance between pole pieces - is on the order of 1 um - 1/25,000 of an inch. As a point of reference, a human red blood cell is about 7 um in diameter and an average sheet of typing paper is about 100 um in thickness. The gap is filled with a nonmagnetic material to prevent it from getting clogged and to force the magnetic flux out of the head structure and into the tape magnetic coating. This remarkably fine spacing is necessary to achieve the multimegahertz video bandwidth.
Actual tape motion for a VCR is remarkably slow. To someone familiar with audio decks, the tape in a VCR even at SP speed (the fastest) seems to be crawling along. Their first reaction is often one of: "there must be something wrong as the tape is moving sooo slooowly." Nope, just amazing technology. The SP speed of a VHS VCR corresponds to a linear tape speed of only 1-5/16 ips - slower than for an audio cassette deck (1-7/8" ips). EP speed is 1/3 of this - 7/16 ips. However, the effective tape speed as seen by the video heads is over 15 feet per second due to the spinning video head drum.
The luminance (Y) and color (C) components of the composite video signal are recorded differently. Luminance, which is in effect the black and white picture with all the high resolution components but no color, is frequency modulated on a carrier at around 3.4 MHz. The deviation is about 1 Mhz and the maximum frequency recorded on a VHS tape is a little over 5 Mhz (Beta is slightly different and S versions of Beta and VHS extend some of these to achieve higher bandwidths. The color signal is separated from the composite video and is amplitude modulated on a 629 kHz carrier. This is called the color under' system. The 'U' in U-Matic, a very popular industrial VCR 3/4" format (which predates Beta and VHS and is still in use) stands for this.
Since the head-tape speed for the VHS audio track is the same high rate as for the video track and exceeds that of a typical audio cassette deck by a factor of more than 100, VHS HiFi audio reproduction - frequency response, signal to noise ratio, and dynamic range - is excellent and approaches that of a CD. In fact, using a T120 video cassette in EP (SLP, 6 hour) mode simply to record stereo music (with the video ignored or blanked) is extremely cost effective. What other media/technology will store a 6 hour concert with nearly perfect reproduction for under $2? (Note: if you do this, some VCRs will require some kind of video input to maintain stable tape speed. You can just ignore the video portion on audio playback.)
There are two disadvantages to VHS HiFi, however: (1) there may be some degradation of video quality due to unavoidable interactions with the buried audio, and (2) it is not possible to rerecord (dub) only the audio without disturbing the video. The only way to do this without copying the video to another tape would be to read out the video and hold it temperorily in a double buffered frame store for subsequent recording back onto the tape after the new video was laid down. However, this would put the video 1 frame behind where it was thus complicating the situation. So, audio dubbing simply isn't supported.
With 8 mm, there is no separate linear audio track - all audio is HiFi using the spinning video heads.
Record: reference signal is vertical sync pulse from video input:
Play: reference signal is timing pulse derived from quartz oscillator:
Really slow speed is usually implemented as a variable frame advance with the tape fully stopping between frames. Special sets of video heads provide the best quality. Freeze frame (PAUSE) uses the same set of heads. As with CUE and REV, acceptable picture quality is provided even with a 2-head VCR for EP speed recorded tapes. In all cases, picture quality can be further improved through the use of a digital frame store.
Note that the servo systems in consumer VCRs are rarely precise enough to implement the kind of instantaneous forward or reverse frame advance that is present in high performance (and high cost) editing decks having jog shuttle knobs with instantaneous and precise response.
Philips/Magnavox used to have a very nice on-line introduction to a variety of consumer electronics technologies. Although their site has disappeared - and even people who work for them have no clue - I have now recovered several of the articles including those on TVs, VCRs, camcorders, satellite reception, and connections. See the Introductory Consumer Electronics Technology Series.
Also check out:
A tech-tips database is a collection of problems and solutions accumulated by the organization providing the information or other sources based on actual repair experiences and case histories. Since the identical failures often occur at some point in a large percentage of a given model or product line, checking out a tech-tips database may quickly identify your problem and solution.
In that case, you can greatly simplify your troubleshooting or at least confirm a diagnosis before ordering parts. My only reservation with respect to tech-tips databases in general - this has nothing to do with any one in particular - is that symptoms can sometimes be deceiving and a solution that works in one instance may not apply to your specific problem. Therefore, an understanding of the hows and whys of the equipment along with some good old fashioned testing is highly desirable to minimize the risk of replacing parts that turn out not to be bad.
The other disadvantage - at least from one point of view - is that you do not learn much by just following a procedure developed by others. There is no explanation of how the original diagnosis was determined or what may have caused the failure in the first place. Nor is there likely to be any list of other components that may have been affected by overstress and may fail in the future. Replacing Q701 and C725 may get your equipment going again but this will not help you to repair a different model in the future.
Please see the document: On-Line Tech-Tips Databases for the most up to date compilation of these resources for TVs, VCRs, computer monitors, and other consumer electronic equipment.
This site includes a relatively short but fairly complete VCR repair guide that covers most of the common classes of problems - with nice diagrams to help with the explanations.
The VCR-only tech-tips database is clearly indexed by manufacturer and model number. Every repair includes a level-of-difficulty rating - which is handy! Many include layout and parts placement diagrams as well.
The developers of this site also sell a variety of generic VCR repair parts, tools, and TV remote controls.
My only real complaint is with respect to the annoying flipping banner at the top of their main pages! :-(
In addition, modern VCRs are NOT built like the Brooklyn Bridge! The weight of a TV or stereo components could affect the VCR mechanically, messing up tape path alignment or worse.
"What are the 'good' and 'bad' brands of videotapes (T-120)? Are the 'extra' or "high" grades really better?"
I would avoid brands you never heard of. K-mart brand, Recoton(sp), the street vendor from whom you buy Chinese food, whatever.
Higher grade tapes are not necessarily worth the expense but in my experience with some like Maxell and Scotch, going one level up from the cheapest is worthwhile and results in a noticeably better picture.
Only a few companies actually manufacture the raw tape stock. For what it's worth (FWIW), I have used Scotch in the past. It was inexpensive and the quality was good and consistent. I haven't purchased video tape in quite awhile now so I do not know if this is still true (Winter 2003).
The higher grade tapes may actually be harder on the video heads due to their formulation but this probably doesn't matter for the ordinary user.. You don't need HiFi grade tapes for HiFi - any tape will work. However, higher grade tapes may last longer with higher quality results in demanding situations like 24 hour a say security monitoring.
Consumer Reports does a review every so often, check back issues. I believe their conclusions were generally to buy name brands by price. Whether you believe in Consumer Reports or not, checking their ratings at least gives you an additional data point.
I have not seen any "official" guidelines on tape longevity for a long time, since the Beta days. Use of old tapes will not generally ruin video heads but may clog them. Proper manual cleaning restores normal operation.
Your mileage really depends on several factors, the most important being the conditions under which it's used. I've seen VCRs that can chew up a tape in one or two passes and make it unusable. High humidity and heat will cause tapes to stick to the head drum and wear prematurely. Shuttling tapes back and forth and leaving them sit in pause (on one spot) can accelerate wear.
Under ideal conditions: clean machine in good alignment running a tape from beginning to end without stopping is as good as you're going to get. Alignment tape manufacturers used to indicate expected life as the "number of passes". No significant degradation in 50 passes, but after that, dropouts become obvious. Maximum life is 200 passes. At that point, the tape is starting to break down with oxide particles being shed onto the heads (actually happens with all tapes to some degree) causing head clogging. With tapes of any age, a liquid spill such as soda pop ends the game right there. It can be cleaned, but unless it's your precious home movies, forget it.
I would use a tape until the dropouts become annoying. Dropouts are places on the tape where the oxide is missing. You'll see them more at the beginning of a tape where it's mechanically stressed by loading and unloading. A lateral scratch on a tape (caused by buildup of gunk in a VCR) will show up as a 3 or 4 line continuous dropout somewhere on the screen. Look at some heavily used rental tapes and you'll get the idea. So, bottom line: use it until it shows it's age. :)
If you want some guidelines, see the next section: Sample VCR preventive maintenance schedule.
Realistically, you are not going to do any PM anyway. So, just be aware of the types of symptoms that would be indications of the need for cleaning or other preventive or corrective maintenance - erratic loading, need to convince the VCR to perform certain operations, whirring motors without completing cycle, VCR taking longer to go into or out of a particular mode than you recall, jittery or noisy picture, or wavering or muddy sound. If your inspection reveals deteriorated rubber parts, obviously these should be replaced regardless of their age.
Of course, acute symptoms like a tape jam or tape munching episode is a sign of the need for emergency treatment. This still may mean that a thorough cleaning is all that is needed.
I generally don't consider cleaning tapes to be of much value for preventive maintenance since they do not run long enough or with enough force to clean the rollers, stationary heads, and guide posts. Also, the dry type, in particular, are abrasive and frequent use may cause premature wear to the expensive video heads.
The following are some reasons to inspect and clean a VCR periodically:
If you follow the instructions in the section: General guide to VCR cleaning and rubber parts replacement, there is minimal risk to the VCR. However, don't go overboard. If the belts are in good condition (by appearance and stretch test), just clean them or leave them alone. This is especially true in the (generally infrequent) designs of some models of VCR tape transports where significant disassembly is required to replace a belt. In this situation, you risk not being able to put everything back the way it was. Most belts can be replaced with little or no disassembly beyond removing the top and bottom covers and possibly any circuit boards that may be in the way, Sometimes one or two additional screws will need to be loosened or removed to move a bracket or shield.
It is not clear here what a 'tape' is though the comments that go along with this table seem to indicate that it means a T120. However, parts that deal with tape loading are affected not by how long a tape is played but by the number of loading cycles. Wear on the video heads, on the other hand is strictly a function of play/record time. Wear of the A/C and erase heads depends on both time and tape speed. Thus, these are additional reasons not to take the numbers below too literally.
After What to do Which parts
------------------------------------------------------------------------------
250 tapes Clean A/C head, capstan, erase head, pinch roller,
impedance roller, supply reel table, takeup
reel table, video heads.
500 tapes Replace Video heads (upper cylinder).
750 tapes Replace Pinch roller
1000 tapes Grease Loading cam gears, impedance roller shaft,
roller guide tracks.
Oil Supply reel shaft, takeup reel shaft.
Replace Reel belt, loading motor belt, main brake
spring, main brake arms (left and right).
2000 tapes Replace A/C head, erase head, supply reel table,
takeup reel table.
2500 tapes Replace Cylinder unit.
Note: if you should ever damage a rental tape as a result of a cranky VCR or for any other reason, don't just give it back to the video store. Please let them know. Also, if your VCR should jam with a tape inside, do not forcibly extract it - read the appropriate sections later in this document. If in doubt, let the video store know what happened and follow their recommendations.
Given that you are not likely to give up the movie couch potato addiction, some problems can be avoided by fast forwarding a couple of minutes into the tape before hitting PLAY. Damage to rental tapes often occurs near the start - and this will avoid some of the useless coming attractions as well!
If you notice the video breaking up or deteriorating while you are watching, immediately ejecting the tape may be the most prudent option since the worst may be yet to come!
While I cannot control your viewing habits, playing a lot of old, dirty, deteriorated tapes (rental or from your own tape library) will eventually take a toll on your VCR. At the very least, you should perform a general cleaning and inspection at more frequent intervals.
(From: Jim Lagerkvist (jlager@tir.com).)
Renting a video tape has all the same potential consequences as renting a hooker. That tape may pass to your machine anything from pizza grease to splices made from duct tape or staples. I keep two VCRs in my house. One for rental tapes and another for known trusted tapes.
Stay away from the line side of the power supply - put electrical tape over the exposed connections. To be doubly sure, tape a piece of cardboard or thick plastic over the power supply section. Other than that, there is more danger of damaging the VCR by accidentally shorting something out or breaking a little plastic doodad than of you getting hurt.
If you get stuck, sleep on it. Sometimes, just letting the problem bounce around in your head will lead to a different more successful approach or solution. Don't work when you are really tired - it is both dangerous and mostly non-productive (or possibly destructive).
Whenever working on precision equipment, make copious notes and diagrams. You will be eternally grateful when the time comes to reassemble the unit. Most connectors are keyed against incorrect insertion or interchange of cables, but not always. Apparently identical screws may be of differing lengths or have slightly different thread types. Little parts may fit in more than one place or orientation. Etc. Etc.
Pill bottles, film canisters, and plastic ice cube trays come in handy for sorting and storing screws and other small parts after disassembly.
Select a work area which is well lighted and where dropped parts can be located - not on a deep pile shag rug. Something like a large plastic tray with a slight lip may come in handy as it prevents small parts from rolling off of the work table. The best location will also be relatively dust free and allow you to suspend your troubleshooting to eat or sleep or think without having to pile everything into a cardboard box for storage.
Another consideration is ESD - Electro-Static Discharge. The electronic components in a VCR are vulnerable to ESD. There is no need to go overboard but taking reasonable precautions such as getting into the habit of touching the chassis first before any of the electronic components is a good practice. The use of an antistatic wrist strap would be further insurance.
A basic set of precision hand tools will be all you need to disassemble a VCR and perform most adjustments. These do not need to be really expensive but poor quality tools are worse than useless and can cause damage. Needed tools include a selection of Philips and straight blade screwdrivers, needlenose pliers, wire cutters, tweezers, and dental picks. A jeweler's screwdriver set is a must particularly if you are working on a portable VCR or camcorder. For adjustments, a miniature (1/16" blade) screwdriver with a non-metallic tip is desirable both to prevent the presence of metal from altering the electrical properties of the circuit and to minimize the possibility of shorting something from accidental contact with the circuitry.
You should not need any VCR specific tools with the possible exception of a miniature metric hex key wrench set for loosening the set screws on the roller guides should you need to perform a tape path alignment. I have never needed a VCR head puller. You can make a tool for the special nut found on many A/C head assemblies for tracking adjustment by filing a slot in the blade of a straight blade screwdriver.
A low power fine tip soldering iron and fine rosin core solder will be needed if you should need to disconnect any soldered wires (on purpose or by accident) or replace soldered components.
CAUTION: You can easily turn a simple repair (e.g., bad solder connections) into an expensive mess if you don't have both a decent soldering iron and the soldering skills to go along with it. If in doubt, find someone else to do the soldering or at least practice soldering on a junk circuit board first! See the document: Troubleshooting and Repair of Consumer Electronics Equipment for additional info on soldering and rework techniques.
For thermal or warmup problems, a can of 'cold spray' or 'circuit chiller' (they are the same) and a heat gun or blow dryer come in handy to identify components whose characteristics may be drifting with temperature. Using the extension tube of the spray can or making a cardboard nozzle for the heat gun can provide very precise control of which components you are affecting.
Basic cleaning supplies include Q-tips (you may know them as cotton buds) for everything BUT video heads, chamois covered cleaning sticks (for video heads), lint free cloths or paper towels, water, and isopropyl alcohol (preferably 91 percent medicinal grade or better).
For info on useful chemicals, adhesives, and lubricants, see the document "Troubleshooting of Consumer Electronic Equipment".
If you have several VCRs or do repairs for friends (former friends?), there are inexpensive kits of VCR mechanical parts like washers and springs that come in handy. General belt or similar kits are not worthwhile unless you are in the service business - there is too much variety in the sizes and other characteristics of these types of parts to make an assortment a good investment.
Note: while working with the top off, you may need to put pieces of strategically located cardboard over the area of the cassette to block extraneous light from causing erratic behavior (modes aborting, not starting at all, etc.) with the start/end-of-tape sensors. Not all VCRs are sensitive to extraneous illumination but I have been bitten more than once by not doing this. Using overhead instead of direct illumination will probably help as well. In extreme cases, placing electrical tape over the end sensors may be needed but this will likely confuse the microcontroller under certain conditions into thinking that a non- existent tape is present - or if your troubleshooting will permit, leave a cassette in the transport. (I have heard of at least one case where this was a problem even for normal operation - apparently, light was falling on the VCR in just the wrong way where it happened to be located. The VCR would enter rewind mode regardless of what the helpless human wanted unless tipped on end!)
A DMM or VOM is necessary for checking of power supply voltages and testing of sensors, LEDs, switches, and other small components. Unless you get deep into the electronic repair of VCRs, an oscilloscope is not required.
There are two items of important test equipment that you probably already have:
(From: someone who would prefer not to be identified).
"Ok, I did something dumb. I was given an old VCR (early 80s) a couple weeks ago (JVC-7100U). It stopped playing and recording, but FF and rewind worked fine. Reading the FAQ, I decided to check it out. I took the top off, and was trying to make the motor run so I could see the problem. There was an incandescent light, and I figured there was a light sensor, so I moved the lamp out of the way. The FAQ suggests electrical tape over the lamp, but I hadn't read it yet. My manipulation caused the lamp to fail. Until I could replace it, I just jumped the connection, which worked fine for awhile. I had just figured out the problem with play/record was a drive wheel not making contact with the take-up reel. It seemed to be a result of a weak spring, and I was trying to figure out which one, when the screwdriver I was manipulating the arm with slipped, and contacted the back side of a circuit board. Lesson number two: Use a chopstick for that purpose. I believe it was at this point I realized I got no reaction from any of the VCR control buttons, so maybe I shorted something out. All the buttons worked before. Even worse, as I was reinstalling the tape loading mechanism, the screwdriver slipped again, in a different place, and I did see a flash when it contacted the back of the circuit board. Whoops."
Don't let this happen to you. Or, at least start out with an old expendable VCR and accept the hits to your pride!
You can buy these for $6-12 but you can make one that is almost as nice:
These cheaters will load and 'play' just fine except that some machines actually sense that the supply reel is being turned by the tape movement during loading or always and will shut down if it isn't (among other peculiarities) so you may have to do this by hand.
There are several benefits to using one of these, one of which is that there is no chance of ruining a prized tape due to a hungry VCR. You will also be able to feel the spindles to get an idea whether they are turning properly and with enough torque in all modes. If you break out enough of the top and bottom, you will have access to the idler and other under-cassette parts at the same time. If you examine one of the commercial cassette cheaters, you will see that very little is needed beyond the outer frame as long as it sits properly on the indexing posts and doesn't jam the mechanism when loading/ejecting.
For general video diagnosis including mechanical and tape eating problems, a bunch of sacrificial tapes is handy - advertising, promos, feature shorts - anything you do not care about but have been recorded on working VCRs. Very often they get mangled and you do not want to continue to use mangled tapes which may damage the VCR - in particular the video heads. However, once you have the VCR basically working, you will want to test it start to finish on a T120 cassette. This is because the reel hub size on those short video cassettes is not the same as a standard (most commonly used) T120 cassette and may mask problems if the VCR is mechanically marginal in some respects.
It is usually very easy to remove the top and bottom covers on VCRs. For the top cover, there are usually some very obvious screws on the back or sides, and in rare cases on the top. There may be a couple of screws on the bottom as well that secure the top cover. For top loaders, you will probably need to remove the cassette holder lid - there will be two screws, perhaps hidden by rubber plugs.
Once all the screws are out, the top cover will lift up or slide back and then come off easily. If it still does not want to budge, recheck for screws you may have missed.
For the bottom cover, there are usually a half dozen or so screws around its perimeter and sometimes in the middle as well. There may be one or two grounding screws as well which are of different length and threads - these should go back in the same location from where they came. Bottom covers are usually simple sheet metal. In rare cases, you will need to remove the front panel to free the bottom cover (or vice-versa).
Circuit boards may prevent access to the top or bottom of the tape transport. Usually, removal of a few screws (often marked with red paint or arrows on the circuit board) and perhaps pressing of a couple of snaps will permit the board to be swung up on a hinge out of the way.
Front panels usually snap off, possibly requiring the removal of a few screws on top or bottom.
Make notes of screw location and type and store the screws away in a pill bottle, film canister, or ice cube tray.
When reassembling the equipment make sure to route cables and other wiring such that they will not get pinched or snagged and possibly broken or have their insulation nicked or pierced and that they will not get caught in moving parts. Replace any cable ties that were cut or removed during disassembly and add additional ones of your own if needed. Some electrical tape may sometimes come in handy to provide insulation insurance as well.
During servicing, a piece of opaque cardboard or other insulating material should be placed above the cassette basket if any strange behavior is detected that was not present with the cover in place. Not all VCRs are particularly sensitive external illumination.
Do not be tempted to use compressed air!
I would quicker use a soft brush to carefully dust off the circuit boards and power supply. Work in such a way that the resulting dust does not fall on the mechanical parts.
For the deck itself, using compressed air could dislodge dirt and dust which may then settle on lubricated parts contaminating them. High pressure air could move oil or grease from where it is to where it should not be. If you are talking about a shop air line, the pressure may be much much too high and there may be contaminants as well.
A Q-tip (cotton swab) moistened with politically correct alcohol can be used to remove dust and dirt from various surfaces of the deck (in addition to the normal proper cleaning procedures for the guides, rollers, heads, wheels, belts, etc.)
Try to locate the part with a bright light without moving the VCR. You may have gotten lucky (yeah, right). Next, over an area where a dropped part will be visible (not a shag carpet!), try any reasonable means to shake it loose - upside down, a little gently tapping and shaking, etc. A hard surface is better in some ways as you might hear the part drop. On the other hand it may bounce into the great beyond.
If this does not work, you have two options:
To prevent this sort of thing from happening in the future you will no doubt be much more careful. Sure you will! Some suggestions to prevent ejection of an E-clip, split washer, or spring into the great beyond:
(From: Paul Sagi (kamrok@tm.net.my).)
For finding a small part dropped on the floor, I darken the room, then shine a flashlight parallel to the floor, with the beam just touching the floor. the oblique (if that is the correct word?) beam shows up the part (and any dirt if the floor was not recently swept!) clearly. this works best on smooth floors or short-pile carpets. on shag carpets, if the part is on top of the pile, instead of having fallen into it (fat hope), the method works also. for shag carpets where the part has tried to hide, shine the light downwards at right angles and imagine how the part would look if seen against the background of the carpet, to prime the mind to recognize it when seen. a strong magnet (for steel parts like e-rings) can help when the above methods fail. sweeping or vacuuming the carpet or floor, then sorting through the debris can also help, especially for non-magnetic parts (sometimes cannot know if the part is magnetic or not until after it is found!)
I do not agree with the advice that a small part that cannot be located often can be left safely inside an electronic device. remember Murphy? he is ever-vigilant and delights in ensuring the part will have fallen where it can do harm when the power is switched on.
Please refer to the photo: Typical VHS VCR Tape Transport Components or Sharp VCR Transport with Major Parts Labeled for parts identification.
The following description applies to 99.9% of the VCRs in existence today. I have seen one that had a sideways loading mechanism - very weird.
Looking at the unit from above with the front toward you:
Some VCRs use gears in place of rubber (as is the case with the VCR shown in the photo: Typical VHS VCR Tape Transport Components. Teeth can break off but these are generally quite reliable. Some high-end decks may have separate motors for reel rotation.
Also on the same assembly are tilted metal guide posts - again one for each side. These sometimes fall out with obvious consequences.
Proper functioning and adjustment of the roller guides is the most critical requirement for proper tracking. (However, do not touch their settings without being really sure that they are at fault and not until you have read the sections relating to tape path alignment.) Clean and inspect.
A hard, shiny, dried out pinch roller can lead to tape edge munching and erratic sound, speed, and tracking. Clean thoroughly. Inspect for cracked, hard, shiny, or otherwise deteriorated rubber, and lack of free and smooth rotation. Replace if any of these are present.
Even if you have no obvious record or playback symptoms, if the pinch roller appears concave or with a distinct worn ridge, replacement is recommended - erratic behavior will soon be the result. A tape which runs off center due to a bad pinch roller may result in tape edge damage and over time can also alter the wear pattern of the audio/control head and various guide posts.
A quick test of the pinch roller is to put the VCR into PLAY and *carefully* try to stop it from turning between your thumb and forefinger - a good pinch roller will not be easy to stop.
However, don't replace a pinch roller that is in good condition. The replacement may be inferior. (Apparently for at least some JVC VCRs, the original pinch roller is of very high quality and will last the life of the VCR if cleaned properly.)
For additional information on replacement rubber parts, see the section: Determining belt, tire, and pinch roller specifications.
The cause for all of these is very often a bad idler tire or other dirty, worn, or tired rubber parts. See the section below: "General guide to VCR cleaning and rubber parts replacement". A VCR that just munched down your favorite tape is very likely only in need of a little tender loving care.
WARNING: Don't turn a simple repair into a full length double feature. Most tires and belts come off without extensive disassembly. However, if your VCR is the exception, DO NOT remove anything to get at the rubber part that may be part of a critical timing relationship - racks or gears, for example - before fully understanding the implications of this action. In some cases, if a gear is rotated even one tooth from where it should be, there can be unforeseen and catastrophic consequences. See the section: Mechanical relationships in VCRs for more information before proceeding any further!
Do not attempt to clean the video heads until you follow the proper procedure given elsewhere in this document, you can break them - very expensive lesson. In most cases, they do not need attention anyhow.
Q-tips and alcohol (91% medicinal is OK, pure isopropyl is better. Avoid rubbing alcohol especially if it contains any additives) can be used everywhere except the video heads. Just dry quickly to avoid leaving residue behind or damaging the rubber parts further.
Cleaning may get your machine going well enough to get by until any replacement rubber parts arrive and to confirm your diagnosis.
Things to clean:
Clean the pinch roller (presses against the capstan in Play, Record, and Search mode CUE and REVIEW) and until no more black stuff comes off. Use as many Q-tips as necessary until no more black gunk collects on Q-tip.
If the pinch roller is still hard, shiny or cracked, it will probably need replacement. Many are available for about $6 from the sources listed at the end of this document. It is sometimes possible to put the pinch roller in an electric drill, drill press, or lathe, and carefully file off the hard shiny dried out rubber surface layer, but only use a last resort - and this fix is probably temporary at best. For a very detailed and complete step-by-step procedure, see: VCR crinkling tape, sound fading, speed flipping. (This is an archived sci.electronics.repair newsgroup posting.)
If the idler tire appears cracked, glazed, or dried out, it will need to be replaced. About $.50 to $1.00. As a temporary measure, you can usually turn the tire inside-out and replace it. The protected inner (now outer) surface will grip well enough to restore functionality until a replacement tire arrives - and verify the diagnosis as to the cause of your problem.
Also, the idler assembly includes a slip clutch. If this weakens, the idler may not have enough force to press on the reel table edges. If it becomes too tight, there may be audio, video, or crickled tape problems and/or excess wear of the idler tire. When in doubt, the entire idler assembly is often available as a replacement part. They can often be disassembled and adjusted if necessary.
Make sure that there are no twists when a square cut belt or replacement is installed on its pulleys.
On some models, you may need to unscrew circuit board(s) blocking access to either the top or bottom of the tape transport. Make notes of what went where - particularly different types of screws and routing of wires.
Any belts that appear loose, flabby or do not return instantly to their relaxed size when stretched by 25% or so will need to be replaced and may be the cause of your problems. Belts cost about $.30 to $2.00 and complete replacement belt kits are often available by model for $3. to $12. Meanwhile, the belts will function better once they are cleaned, maybe just enough to get by until your replacements arrive.
While VCRs should be cleaned periodically, the video heads themselves usually do not need cleaning unless you have been playing old or defective rental tapes which may leave oxide deposits on the tips of the delicate ferrite head chips. Unless you are experiencing video snow, intermittent color, or loss of or intermittent HiFi sound (HiFi VCRs only, the HiFi heads are located on the video head drum and for the purposes of cleaning, treated the same way) leave the video heads alone.
If you really feel that video head cleaning is needed, refer to the sections on video head problem diagnosis and cleaning elsewhere in this document.
I pride myself on the cleanings I do with all repairs, I like to keep my shop up to command performance and a cut above the rest I usually even clean up the chassis and deck of most equipment and relubricate and all the trim.
I have seen my share of broken heads come in from people after they use a Q-tip...or a store bought cleaning tape...
I use a few different size hemostats with a folded up lint free cloth. When
folded, it really buffs the cylinder units and leaves a nice shine on the tape
guide rollers, and audio and erase heads too. I have cleaned a head with
chamois swabs and then gone over them with my own cloth and was horrified to
see the residue that was left from ordinary swabs, when it was all collected
on the cloth. It doesn't snag the video or stereo hi-fi heads either - I
have cleaned a few thousand this way and never snagged any
I use generation 2000 disk cleaner for heads and acetone to degrease the posts
and capstan - just a dip - not too much.
(Editor's note: take care with strong solvents like acetone - both to protect
your health and avoid damage to plastic parts. --- sam)
Pardon me while I trip over my long gray beard :-).
In the old days, we used to clean the platters in a disk drive using what were
essentially tongue depressors wrapped with a Texwipe (Lint-free paper). We
would first use 99% pure isopropyl alcohol and follow it with freon. (AAAAAh!
the Ozone layer!) We would then manually run the heads out over the platters
(while they were spinning) and listen for 'ticks'. If we heard any, we'd
repeat the process. For those who smoked in the computer room, the residue
could build up rather thick and evenly. Getting the whole mess off was a
chore. If such was the case, I actually would use Soap and water, followed by
water, then the alcohol and finally the freon. (This was more like R-22 and
not the R-12 variety. That, we used do dump into the atmosphere freely trying
to cool down components.)
I have resurrected many road-kill VCRs by using those cleaning techniques on
them. I haven't as yet had to use soap, but using other than alcohol proves
beneficial. Just don't get too liberal with any of the cleaning fluids. By
the way, the freon was used to remove any residue left behind by the alcohol.
NEVER, ever, use WD40 in a VCR! WD40 is not a good lubricant despite the
claims on the label. Legend has it that the WD stands for Water Displacer -
which is one of the functions of WD40 when used to coat tools. WD40 is much
too thin to do any good as a general lubricant and will quickly collect dirt
and dry up. It is also quite flammable and a pretty good solvent - and there
is no telling what will be affected by this:
(From: Matthew Fries (freeze@visi.com).)
A light machine oil like electric motor or sewing machine oil should be
used for gear or wheel shafts. A plastic safe grease like silicone grease
or Molylube is suitable for gear teeth, cams, and the roller guide tracks.
Unless the VCR was not properly lubricated at the factory (which is quite
possible), the only likely areas needing lubrication are the roller guide
tracks - clean and grease. Sometimes you will find a dry capstan, motor,
lever, or gear shaft but this is less likely.
In general, do not lubricate anything unless you know there is a need.
Never 'shotgun' a problem by lubricating everything in sight! You might
as well literally use a shotgun on the VCR!
For the following, do not go near the video head drum, only perform
demagnetization of the stationary A/C head, erase head, and guide
posts and rollers. In my opinion, the video heads should almost never
need to be demagnetized. The ferrite material from which they are
constructed is not prone to easily being magnetized like steel.
Use a small demagnetizer designed for a tape deck or cassette deck.
Do not use anything homemade that might be too powerful or a bulk
tape eraser which would certainly be too powerful.
Make sure the tip is covered with a soft material to prevent damage to
the finely polished surfaces in your VCR.
Turn power on to the demagnetizer when a couple of feet away from the VCR.
Then, slowly bring it in close and slowly go over all surfaces of anything
that the tape contacts or comes close to in the tape transport. The key
word here is **slowly**. Move fast, and you will make the magnetic
fields stronger. When finished, slowly draw the demagnetizer away to a
distance of a couple of feet before turning it off.
Use a large nail with its point filed down to a blunt tip covered with
tape or a plastic or rubber boot to protect the polished surfaces of the
heads. I have no idea of the exact number of turns but I'd say start with
100 turns of #20 to #26 AWG insulated wire. There should be a noticeable
vibration when bringing the tip with 1/4 inch or so of a ferrous surface
but not much beyond this.
CAUTION: This may be too strong for the video heads - stay away from them!
In fact, it may be too strong at the full 12 VAC. A lower voltage adapter
may be better or use on a Variac. If it pulls nails out of your drywall,
it's too strong. :) Use at your own risk!
(From: Steven L. Bender (buqu35d@prodigy.com).)
You need a Power Transformer about 3" in each direction, can be like a
low voltage 12 volt / 3 Amp unit or rated higher. Remove end bells if
any, remove all the metal laminations (break the first one, yank it,
and the rest will come easier). Re-insert all the metal laminations
facing in the same direction, with the "E" all pointed the same,
re-glue, varnish, or whatever. Connect AC Plug to the Primary, then
insulate the whole works with Plastic tape and outre layer of Duct
tape. After insulating it with several layers of tape - Instant Bulk
Eraser.
Warning - Do not apply power for more than 60 seconds at a time! (It will get
hot and burn your hand after two minutes.)
I had one of those for some years, but accidentally left it plugged in,
(pulled the wrong wire out of the 6 to 1 outlet box) and after a few
minutes, it smelled and was too hot to touch, and made a nasty noise as
the copper started to melt... (Sounds Effects of Liquid Krell Metal
in the distance...., Forbidden Planet - Paramount, 1956).
Luckily I didn't walk out, another few minutes and it would have caught fire..
I am not liable for any personal, profession, or consequential damages from
use of this information !!!
(From: Steve Walz (rstevew@armory.com).)
Use a transformer and remove the EI core pieces and replace all the E's
only in the same direction. Current limit it with a wire-wound resistor
so it doesn't overheat and put a momentary pushbutton on it and a power
cord to wall AC and insulate it so you don't shock yourself. Then place
it so the open face of the E core pieces faces the tape or disk or
whatever to be erased and push the button. Run it all over both sides of
the tape or disk and pull the tape or disk away before letting up on the
button if you wish to erase it. If you wish to magnetize a tool or such,
simply let up on the button while the object or tool is still in contact
with it. That's how that works! (You may have to do it a couple times before
you catch the AC cycle at the peak! --- Sam.)
(From: Pat Swayne (me@patswayne.com).)
Here's a safety tip for your homemade bulk tape eraser: Use a small length
of very thin solder as a fusable link. Place this as close to, but
insulated from, the primary windings as possible, and pass the current
through it. If the thing gets too hot, it will melt the solder and break
the connection.
(From: Sam.)
It would have to get mighty hot for that to be effective but it's cheap
enough. Of course, a thermal fuse or thermostat would be a more well
controlled alternative.
If attempting to load a cassette produces no response (though the
VCR has power), then there could be a problem with the microswitch that
senses the presence of a cassette, the cassette loading motor (if separate
from the main motor), a slipping or broken belt, or a faulty driver
or other electronic problem. Sometimes this could mean that the
microcontroller is confused due to a faulty mode switch or because
the mechanism somehow got into a peculiar state. Manual cycling of
the cassette loading mechanism might reset it. Gently push a cassette
in and turn the appropriate shaft or pulley by hand. First, try this with the
VCR unplugged. If nothing happens or you feel resistance, try the
other direction. Assuming you find no problems - there is no significant
resistance to your turning and the cassette basket cycles from fully
ejected to fully seated on the transport baseplate, leave the cassette
basket in a partially loaded position and plug the VCR into the AC power
and turn it on (this may not be necessary depending on the design of your VCR).
It should now reset itself and either load or eject the cassette.
If there are still no signs of a response, a power supply, motor, or
electronic problem is likely.
Note: If this only happens with T160 (8 hour) tapes, it may be a problem
with the thinner tape confusing the sensors. Avoiding these tapes is really
the best thing to do since they can cause all sorts of problems (especially
if they are an off-brand and of inferior quality to begin with).
If you hear a motor whirring but nothing happens, this is almost certainly a
slipping or broken belt or something blocking the proper movement a mechanical
part.
If pushing a cassette into the VCR results in it being ejected as though
it tasted really bad (there may or may not be hesitation), or if the cassette
cycles back and forth without stopping, there could be several possible
causes.
If it stops part way during loading, does it pause as though the motor
is straining or just abort with no warning? If the former, then check
carefully for foreign objects, or lack of lubrication. A typical cause
is a belt slipping, usually not the idler in this case. Help it out gently
and see if that will complete the cycle. Sometimes it is helpful to cycle
the mechanism by hand - turning the appropriate shaft or pulley and feeling
and watching for any place where it binds. If the basket moves in the wrong
way or you feel any significant resistance, try the other direction.
Sometimes, the sticky cassette labels partially or totally peal off and
clog the works. You may find a toy or rock inside carefully inserted by
your 3 year-old! A bit of the cassette shell might have broken off and
jammed the mechanism just to confuse you!
If the microcontroller were detecting an abnormality, then it would abort
instantly but would most likely try to unload the tape before giving up
but not in all designs. It is possible that if the expected behavior is
not produced by the end/beginning-of-tape sensors during cassette loading,
an abort could be initiated. Therefore, these sensors could be suspect.
In some cases, the mode switch may be dirty or faulty. A gear may have
broken some teeth or slipped a couple of teeth and the timing relationships
may be incorrect. There may be a microswitch that is controlled by the
cassette basket position and this may be defective or dirty.
Similarly, if the cassette seems to be cycling in and out in an apparently
infinite loop, there may be an obstruction or the microcontroller is confused
by a bad sensor or the basket is out of synchronization with the rest
of the mechanism. A squirt of contact cleaner into the microswitch sensor
and/or reflowing its bad solder connections may solve this type of problem.
Similar comments apply to cases where pressing the EJECT button
produces no response. In particular, if the cassette was loaded
successfully and you just finished a thoroughly enjoyable movie,
the microcontroller may think the mechanism is not safe and is not
ejecting to protect your valuable tape from possible damage should
it not be fully retracted into the cassette. As with loading, EJECT
may result in partial movement and shutdown or reloading the cassette
into the down position. All the same causes apply.
There are even some poorly designed VCRs where extraneous light through the
vent holes or tape door affect sensors and cause erratic operation. If a
bright light is shining on the VCR, block and see if anything changes!
To remedy the underlying problem, see the sections on: "Cassette loading
and eject problems" and other for appropriate information. This section
only deals with getting the cassette out without damaging either your
valuable recording or VCR.
Under no circumstances should you force anything - both your tape and your
VCR will be history.
First, see if the VCR just got into a confused state - pull the plug and
patiently wait a minute or two. This may reset the microcontroller and all
will be well. These things happen.
If this is not successful, you will need to open up the VCR (unplug it
first!) and attempt to cycle the mechanisms by hand. Probably both top and
bottom covers will need to be removed. The following procedures assume that
there are no broken parts, foreign objects, or other damage which might
prevent manual cycling of the tape loading and cassette loading mechanism.
(Inspect for toys and rocks.) Also note that some VCR designs use solenoids
to engage various operations. This will complicate your task (to put it
mildly) as locating and activating the proper ones at the appropriate time
is, well, a treat.
If a single motor performs both the tape loading and cassette loading
functions, stop turning as soon as you see the cassette start to rise
and read the next section before proceeding.
If you are not fully successful or if there is still a tape loop outside
the cassette even once you have been turning for what seems to be an
eternity, you can still try to eject the cassette but will need to be
extra careful not to crinkle the tape as the cassette door closes with
the tape sticking out. Before proceeding on in this case, try to find
a way to turn one of the reels to pull that tape back in as this will
make your task a lot easier. There may be an idler that swings between
the two reels and this may be accessible from the bottom (the cassette
will block it on top).
On a top loader, there is usually a solenoid specifically for EJECT or
a simple mechanical pushbutton. Once the appropriate lever is pressed,
the cassette should pop up - hold the basket with one hand as you do this
to prevent any exposed tape loop from being crinkled.
On a front loader, locate the cassette loading motor and begin turning
it in the appropriate direction - this will be fairly obvious assuming
there are no broken gear teeth or other broken parts and that something
isn't totally jammed. If this is the main capstan motor, then just
continue turning as in (1). Eventually the cassette should raise up
and out.
As above, applying external low voltage power (6 to 12 VDC) to the motor
*after* disconnecting it is an alternative if you cannot gain access to its
shaft to turn it by hand.
If you have a tape loop, be extra careful not to catch it on any
guideposts or obstructions as you remove the cassette. Then, wind it back
into the cassette by turning one of the reels (you may have to depress the
release button on the bottom of the cassette with a pencil - this is the
small hole in the center near the label side.)
And in some cases, just turning the VCR upside-down and gently easing the
cassette out will work. But as noted, don't force anything.
Assuming the tape is not torn and not badly crinkled, it should be fine.
If it is severely damaged, refer to the section:
Recovering damaged or broken tapes.
Assuming that the problem is still present, here are two suggestions:
If there is some underlying problem which caused the basket to be
lowered without a cassette in place, than the VCR may return to the
illegal state, do nothing, or do something else that is peculiar
once power is restored or any button is pressed.
For additional info on initialization problems, see the section:
VCR is failing the power-up sequence.
Anyway, rule out the idler tire as well as the idler clutch - if it
weakens, then the idler wheel does not press against the appropriate
reel with enough force to grip.
Is it s top or front loader? If a top loader, you should be able to
trick it into playing a nonexistent tape by covering up the end-of-tape
light (the one sticking up in the middle) so that it will think there is
a tape inserted. (In some models, there might also be a microswitch.)
This may permit you to see what is going on.
If a front loader, then it is tougher. You need a cassette cheater
(see the section: Cassette cheaters).
Then, with the cheater in place happily fooling the VCR, feel the
spindles while the machine is operating. In FF or REW, you may
find that they are not being driven or or being driven very weakly.
Try to determine if the idler is even being pushed into position or
is hung up on something.
If there is any chance that it is the idler tire, try turning it inside-out.
The relatively protected inner (now outer) surface may grip well enough to
confirm the diagnosis.
Has it been serviced in the last 15 years? The last 100 years?
Make sure the tape is not the problem - try another one.
If it starts the operation (as evidenced by whirring sounds and the tape
counter changing numbers) but at some point - perhaps near the end of
the tape - aborts and shuts down, then a worn idler tire, worn or broken
idler clutch, bad belt, or lubrication problem is likely. See the section:
VCR will not fast forward and/or rewind
as well as Lubrication of a VCR.
With instant start transports - where the tape is maintained around
the video head drum for all but the fastest rewind, there could be
other control problems as well.
If the tape starts fast forwarding or rewinding properly (from a visual
inspection with the cover off) but the tape counter does not change value
and then the unit shuts down, a reel rotation sensor problem is likely.
See the section: Reel rotation sensors.
If the operation aborts at the same location on only certain tapes, there
could be pinholes in the tape oxide coating allowing light to pass through
and confuse the sensors. This happens mostly with T160 or old well worn
tapes. If you can locate the problem area, you can try indelible ink on the
NON-oxide side of the tape but DO NOT use adhesive tape or glue. Else,
discard the tape or live with its behavior.
First confirm that the same thing happens with more than one cassette - it
could be defective.
(Portions from: Alan McKinnon (alan.mck@pixie.co.za) and Oldguyteck
(edward.croteau@the-spa.com).)
You get several types of noisy rewind:
Miscellaneous causes:
The list goes on and on. In the end, the only way to narrow down the problem
will be with your eyes and ears!
I would not bother with a rewinder just to prevent wear and tear on the motors
or heads.
In more detail, assuming a 3 minute rewind time for a T120 tape (total tape
length 240 m), the linear tape speed for REW or FF is 80 m/minute or 1.333
m/s. Relative video head-tape speed in normal play is about 4.83 m/s. So,
the 1.333 m/s (actually, due to the slant of the tracks, it is very slightly
less) gets added (REW) or subtracted (FF) from 4.83 m/s. So, assuming
the machine is properly adjusted) this is similar to an equivalent length of
time in normal play and is really is negligible. I wouldn't lose sleep
over video head wear in this case or get a rewinder just to save wear on
the video heads.
If the convenience of being able to rewind off-line is important to you, then
there may be no harm in using one. However, some rewinders can be hard on
video tapes as they usually do not sense the clear leader but stop rewinding
when the tape tension increases at the end of the tape. This may eventually
damage the tape and/or pull the tape from the takeup reel hub. I have heard
of some crinkling the tape edge and actually mangling tapes.
(From: Jim Lagerkvist (jlager@tir.com).)
There are dozens of fast rewinder units claiming to save wear on your VCR.
The earliest ones snapped-off the clear leader from the hubs. The later ones
with IR sensors simply made the real problem obvious:
Precious recordings are being damaged by a cheap transport screaming the tape
at high speed. The tape is either creased or an edge is rippled (usually the
control track).
I have a long list of heartbroken people that have lost their archives with
these things; me included. If a customer complains about a tape suddenly not
viewing well, ask if they use one of these things.
See Some Locations for VCR Mechnical Problems
parts identification in a typical transport.
Check all the belts above and below the deck. Belts can appear to
be firm but if they do not return immediately to their relaxed length when
you stretch them 25%, they will need to be replaced.
With the cover off, observe the behavior when you hit play. (You may need
to put a piece of cardboard over the cassette to block external light from
interfering with the start/end tape sensors). Assuming this is a basic VCR
(no instant start features), you should see:
With a 'rapid or quick start' (or it may be called something else) transport,
the tape moves to a half-loaded position when the cassette is inserted.
This is at an intermediate position partially pulled out of the cassette
but not wrapped around the drum. On VCRs with a real-time counter and/or
index search capabilities, the tape will be in contact with the control head.
With an 'instant start' transport, the tape will fully load around the
spinning drum when the cassette is inserted but the capstan will not engage and
no tension will be applied to the tape until you press PLAY or REC. (After
about 5 minutes, the drum will stop and it may unload to the half loaded
or unloaded position.)
Note that for VCRs with a real-time counter and/or index search capabilities,
the tape must be in contact with the control head (but not the video heads)
for all relevant modes. These VCRs (which include many modern units)
must therefore pull the tape at least partly out of the cassette.
In all cases, the completion of the sequence results in approximately
the same mechanical configuration during PLAY.
Several likely possibilities when it shuts down:
Make sure the tape is not the problem - try another one. There may be spots
on the tape where the oxide has come off resulting in pinhole (or larger) areas
which are activating the end-sensors.
Confirm that you are using the proper play or record modes - not OTR (One Time
Record) or other timed play or record modes which will likely operate in
increments of 15 minutes depending on how many times you press the button.
In addition, on certain VCRs, if the program timer is enabled with a program
setting that has its stop time occur while you are using the VCR - even if
the record operation has been aborted by pressing the stop button - the VCR
will shut down.
If play or record aborts at the same location on only certain tapes, there
could be pinholes in the tape oxide coating allowing light to pass through
and confuse the sensors. This happens mostly with T160 or old well worn
tapes. If you can locate the problem area, you can try indelible ink on the
NON-oxide side of the tape but DO NOT use adhesive tape or glue. Else,
discard the tape or live with its behavior.
Finally, make sure you are not using any 'insert editing' modes which require
a previously laid down control track and would abort once blank tape was
reached. See the section: Recording stops at random
times on previously used tapes.
Once all the obvious problems and cockpit errors have been eliminated,
mechanical problem still likely even though the VCR does not abort
immediately. A worn idler tire, worn or defective idler clutch, bad belt,
or improperly adjusted backtension, are all possibilities.
This is particularly likely if the problem is more likely to occur or only
happens near the end of tapes as the required takeup reel torque is greater
and any of the above mechanical problems will be exacerbated.
With instant start transports - where the tape is maintained around
the video head drum for all but the fastest rewind, there could be
other control problems as well.
If the operation starts properly (as indicated by a changing picture on the
TV in play or from a visual inspection with the cover off) but the tape
counter does not change value and then the unit shuts down, a reel
rotation sensor problem is likely. See the section:
Reel rotation sensors.
This could still be due to problems similar to those which cause an
immediate abort if some components or connections are marginal. Also
see the section: VCR aborts play or record
during startup or shortly thereafter.
If your VCR aborts playing unexpectedly and shuts down and then, pushing
EJECT results in a tape loop hanging out of the cassette when it is
removed, this is considered tape eating - refer to the section:
VCR eats tapes. However, if all other functions
work normally but ejecting results in a tape loop, this section is for you.
Using a garbage cassette, try to observe exactly what is happening
during EJECT. Specifically, is the operation terminating early or
is there some problem with the appropriate reel not turning or not turning
reliably or quickly enough? Is the tape getting hung up on the roller
guides or on some other guideposts?
As with tape eating, the most common cause is dirty, old, deteriorated
rubber parts - particularly the idler tire - preventing the tape from
being fully wound back into the cassette. Therefore, the first step is
to follow the procedures in the section "General guide to VCR cleaning
and rubber parts replacement".
If this only started happening after you had the VCR apart for any reason,
recheck your work - you may have neglected a connector, have the mode
switch slightly out of position, or have gears which are improperly timed.
Many VCRs determine that the tape is completely wound back into the
cassette by sensing rotation of the non-driven reel indicating that
the tape is pulling on it as a result of being tight and pulled by the driven
reel. If this sensor is defective, disconnected, the signal is noisy,
or the associated electronics are faulty, the operation may be terminating
early. As an experiment to confirm this, use a cassette cheater and
while the VCR thinks it is winding the tape back into the cassette, turn
the non-driven spindle by hand - this should stop the operation instantly.
If it stops too quickly - before you turn the spindle, there could be a
problem with this sensor. It is also possible for a failure of one of
the reel brakes to allow one of the reels to continue spinning even after
motor power has been shut off. Alternatively, a sticky brake band may
increase the driven reel torque and fool the microcontroller into thinking
that the tape slack has been taken up.
If the roller guides get hung up on the tracks while being retracted,
even for an instant, the tape may become tight around the roller guides,
pull on the non-driven reel, and stop the operation before the tape is fully
wound back into the cassette. Check for obstructions and for adequate
lubrication of the roller guide tracks.
If it is a late model Sony, the 'half loading arm' could need lubrication.
See the section: Late model Sony VCR munches tape on
eject.
With some VCRs, this may also result in periodic slowing or pausing. See
the section: Sony capstan motor (bearing) problems.
There can be a variety of causes for this behavior but the most likely is
related to a dry or worn capstan bearing or a defective capstan drive/servo
circuit. The capstan rotation almost entirely determines tape movement
during play and special effects modes. Only if for some reason the supply
reel cannot rotate at all, could the capstan attempt to pull the tape across
the video head drum unsuccessfully.
If you can catch the VCR in the act, then there are several tests that can
be performed easily to localize the cause:
Cleaning and lubrication will help. Whether this is a permanent cure will
depend on the severity of the damage.
Adjust the position of the sensor. It's hard to say from here how far away
it can be but as a start, you should be able to slip a piece of letter paper
between the sensor and the rotor without it rubbing at any position of the
rotor.
Inspect the belts and replace if necessary. In the meantime, clean the belts
and pulleys which should result in some improvement and confirmation of the
cause of the problem.
You will have to determine what is preventing the tape from being fed
properly. There could be a broken part, a problem with the supply reel or
some other bearing, or something else like a defective brake release
solenoid or its driver.
(From: Frank Fendley (frank.fendley@datacom.iglou.com).)
To see if the bearing is the problem, I usually remove the bottom cover
of the VCR, play a tape for a fairly long time (or until the symptoms
pop up), and then flip the VCR over and check the temperature of the IC
on the capstan motor circuit board with my patented index-finger thermal
probe. If the IC feels "hot", as opposed to warm or even very warm,
I'm pretty confident that the bearing is at fault. (I define "hot"
as too hot to leave my finger in place for more than a couple of seconds).
If the IC doesn't feel excessively warm after the symptoms start, I would
suspect a heat problem in the servo section. This could be a tough repair,
unless a can of freeze spray proves helpful in pinpointing the component.
If it is not the backtension, check free rotation of the drum when it stops -
I bet it turns as freely as always. Could be a part in the motor driver
that is faulty and failing when hot. However, the bearing could be worn
or dry which would require disassembly and lubrication or replacement of
the lower cylinder (assuming this is where the drum bearings are located).
Usually under humid conditions, but not condensation of tape path,
tape has excessive amount of drag around the scanner. S-tension is
OK, or even a little light, but there is so much drag around scanner
that the capstan skids.
None of these is a *real fix* and the problem recurs eventually.
Somewhat dependent on the tape, but real problem appears to be drag
around lower drum. Anyone know of a fix other than a new scanner?
(From: Daniel Schoo)
This seems to happen mostly on machines with a lot of play time. There
is supposed to be an air film between the tape and drum to facilitate
the reduction of friction. When the drum gets worn and polished the air
is squeezed out and the tape sticks. Little can be done for this. You could
replace the drum but this is expensive and not worth the effort for most
machines. The other option is to try and rough up the drum surface by light
sanding with 3M Scotchbrite(tm). I don't need to go into detail about how
difficult this is to do correctly but what the heck you don't have anything
to loose. Just be careful and stay clear of the heads. BTW I have seen
"cleaning" tapes that rough up the drums very well!
Picture jittering vertically may be similar problem. Tape is not moving
smoothly over the head drum.
This could mean many things including motor problems as well as a general
power supply or control system failure. However, here are a several things to
try first:
Consult your user manual if in doubt about how the thing is supposed to
work!
If any of these appears to solve the problem, it is quite possible that you
will never experience it again. However, a dirty mode switch (see the
section: VCR mode (sensor) switches may have
resulted in an overshootto a bad mechanical state and without cleaning
or replacement, the same thing may happen again.
Unfortunately, this probably isn't much help since identifying and locating
the relevant components will be next to impossible without a schematic :-(.
However, first try unplugging it for 30 seconds or so and plugging it
in again. The microcontroller may just have had a bad day and gotten
confused - either a bad reset or a power glitch.
Assuming this doesn't help:
This could be due to a faulty end sensor or a bad LED or light bulb
that provide illumination for the end sensors.
If either sensor's output is the same as when a cassette is present
(blocked), it very likely that the microcontroller will be confused.
In some designs, this is indistinguishable from a cassette actually
being loaded.
If the 'cassette in' indicator is on, then this is likely.
BTW, if a VCR uses an actual light bulb for that central light source
and it is not lit when you attempt to load a cassette, it is burnt out.
The LEDs used in most modern VCRs are IR and invisible, however.
With somewhat similar symptoms, it is also possible that the VCR is not
able to complete the startup initialization due to a slipping belt,
gummed up lubrication, or other mechanical or motor problem.
The clincher would be if you manually load a cassette (by turning the
appropriate pulleys, etc. with it unplugged) and it then plays the cassette
properly and acts normally until you try to eject. However, don't try
this unless you are sure of how the mechanism works as it is easy to
cause damage.
Before you break out the screwdriver or shotgun, cover up the IR remote
sensor and cassette slot. Some types of electronic ballasted fluorescent
lights may confuse the remote control receiver. Or, someone or something may
be sitting on the remote hand unit or it may be defective and continuously
issuing a REW command! Excessive general illumination may even make its
way into the tape start and/or end sensors and trick the VCR into thinking
the tape is at one end. (If you are working on the VCR with its cover
removed, block any stray light from hitting the area of the tape transport
to see if behavior returns to normal.)
Assuming neither of these is the source of the problem:
First, eliminate the possible mechanical causes such as slipping belts or
a bad idler tire which could prevent the VCR from completing your requested
action - it then shuts down or attempts to return to a 'safe' position.
Bad connections are a possibility but not as likely as in a TV or monitor,
for example. However, some VCRs (certain JVCs and clones, for example)
ground parts of the circuitry via the circuit board mounting screws and
simply tightening these are all that is needed to affect a cure.
The microcomputer or its associated circuitry could be defective as well - but
this is not as common most people fear.
Occasionally, a faulty power supply may result in similar behavior. Its
output voltages may be marginal, drop under load, or have excessive ripple
due to dried up filter capacitors.
However, a more likely possibility than any of the above is that a sensor
assembly present on most VCRs called the 'Mode Switch' or 'Mode Sensor' is
dirty or bad. See the section: VCR mode (sensor)
switches. Failure of the Mode Switch is a very common problem with
numerous VCRs of many makes and models.
The microcomputer monitors the outputs of the Mode Switch continuously when
it is executing a mechanical operation (some monitor it at all times even
with power 'off'). If an operation takes too long to move from state to state
or an incorrect state transition occurs, the operation will be aborted and
an attempt - possibly several - will be made to return the transport to a
'safe' position - unloading the tape and possibly ejecting the cassette.
Most Mode Switches are actually mechanical rotary or linear switches with
sliding contacts. However, some VCRs use optical Mode Switches - IR LEDs, a
slotted wheel or sliding mask, and photosensors. These are much less common
and failures are even less likely. Most of the specific comments on below
on cleaning and so forth apply to the mechanical variety.
See: Studio
Sound's Mode Switches Page for some photos of typical units.
If the Mode Switch contacts are dirty or worn, or if it has somehow loosened
on its mountings and shifted slightly, one or more of these positions will
report back incorrectly or erratically signaling an error condition. For
example, a transition from state 1 to state 4 directly would totally confuse
the poor controller. A Mode Switch that shifted out of place (or where
other timing relationships in the VCR are messed up) might result in certain
operations stopping at the wrong position as well. For example, if the
Mode Switch shifts one way, the pinch roller may never quite press against
the capstan or the roller guides may not snuggle up to the V-Stoppers as
they should in play mode. If it shifts the other way, operations may fail to
complete and run against the mechanical stops - stripped or broken gears may
even the result.
A dirty or worn mode switch can result in cassette or tape loading, or
unloading or eject operations aborting and resetting or the VCR shutting
down. For example, some Emerson VCRs will move part way when loading and
then shut down. Repeated attempts may get them fully loaded and then PLAY
or other tape movement operations will work properly. However, unloading
will result in similar cranky behavior.
Note that erratic behavior that happens after the tape has been playing or
recording for awhile is probably not mode switch related since nothing is
changing in terms of mechanical relationships and the mode switch is probably
happy. However, there can always be exceptions.
Mode Switches are usually linear or rotary slide switches with 4 or more
output terminals. They may or may not be easily accessible. On some, they
are visible once the bottom cover is removed. On others, they are buried
beneath a bunch of mechanical doohickies (technical term). Some are
removable with a screw or two and a connector. Others require desoldering
and the removal of a whole lot of stuff - all of which must be carefully
replaced with exactly the same timing relationships - just to gain access.
Once, you get at them, you can often snap apart the housing and use contact
cleaner on the sliding contacts and surfaces. I usually do not use any
kind of lubricant as it can gum up on the contact surfaces resulting in
erratic outputs - possibly the cause of the original problems in the first
place. Some may not come apart and replacement is the only option if
squirting contact cleaner through any visible openings does not help.
Note that without disassembly, there is no way of knowing if there is
still dirt or gummed up grease inside or if the contacts are actually
pitted. Conversely, if squirting in some contact cleaner does not help,
the mode switch may still be the problem since you have no way of knowing
how far the contact cleaner penetrated or whether it had any effect.
Sometimes, bad solder connections to the mode switch are the only problem.
However, be very careful about not moving anything and take careful notes
on the position of any parts that you disconnect as critical timing
relationships are controlled by the gear positions. Stripped gears or
other broken parts may result when the mechanism cycles. Also, in certain
positions, levers or sliders operated by the mechanism you remove may
spring out of position and you will need to make sure they get put back
into the correct slots in any cams when you are done. Mark all gear
positions even if they do not seem to be critical. See the section below
on how not to mess up your day by ignoring timing marks or more simply:
"Mechanical relationships in VCRs".
Note that if you experience erratic behavior with a VCR manufactured
by Sharp, the probability of a dirty mode switch is very close to 1.
See the section: Erratic behavior of Sharp VCRs.
There are even some poorly designed VCRs where extraneous light through the
vent holes or tape door affect sensors and cause erratic operation. If a
bright light is shining on the VCR, block and see if anything changes!
Note: if this only happens while servicing, confirm that excessive light is
not affecting the start/end sensors.
Do not confuse these sorts of symptoms with those indicating a faulty or dirty
mode (sensor) switch. See the section: Erratic behavior
in various modes.
Exceptions include:
CAUTION: Always try to avoid pulling on the wires when removing a connector.
This will minimize stresses which could result in the wire conductor breaking
off inside the insulation - this would be very difficult to locate.
Assuming that 'forcibly' does not mean that permanent damage was done, then
the first place, as always, to check is the idler tire and then all other
rubber belts. At this point it is hard to say whether your problem was
compounded by the removal of the tape. If any gears were shifted with
respect to one another, parts bent, or springs sprung, then without a
service manual, it would be difficult for a technician let alone someone
not familiar with your VCR to repair it.
An error at power on usually means that the microcomputer thinks that it is
unable to put the mechanism into a 'safe' position. This could be due
to slipping belts, broken gears, a bad motor, shifted sensors, or faulty
electronics. The original symptoms may have been a slipping idler preventing
the takeup reel from rotating allowing tape to spill into the machine.
Power on problems may be more serious. See the section:
VCR is failing the power-up sequence.
(From: AL (kb8wcq@tir.com).)
"I have a Panasonic VCR (model PV-4820) that will not acknowledge tapes.
The original problem I found was in the power supply. I replaced all
the electrolytic caps, and the PS now works- all the outputs measure OK
and the display and tuner controls seem to work OK.
But once the PS went bad, it would not take in tapes, so the owner
decided to force one in. He sheared half the teeth off of the
'link gear', which I replaced, but it still will not accept a tape.
I can manually push a tape all the way in, with some resistance,
until it sits down on the reels, but it is not acknowledged in any
way. If I don't hold it down, it springs back out."
It sounds like you possibly failed to retime the link gear in relation to
the rack gear on the loader assembly.
If that's the one I think it is and you have not timed one (of course this
is something the average person does, say once a week? :-) --- sam)
before, you probably should get the manual. Or try this: Remove the
carriage assembly, turn the VCR on its side, press and hold the little
height change lever (bottom side, near the solenoid), manually turn
(CCW) the large belt-driven pulley until the mechanism is in the full
eject position, note the position of the link gear, turn the large
belt-driven pulley in the opposite direction until the link gear makes
exactly one revolution, re-install the carriage (in the eject position)
making sure the carriage gear and the link gear mesh properly.
Other than that it's pretty simple... Assuming of course nothing was
disturbed with the gears below the deck, and that the link gear, mode
switch, pressure roller lift cam, etc', are in their proper position.
Sounds simple enough! --- sam :-)
On a VCR which has been cleaned and with good rubber parts:
VCRs have a light or LED (IR, infrared) in the middle of the mechanical
assembly that detects the end of tape. When a tape is loaded the
tape will cover the sensor. The controller can tell if the tape is at the
beginning, middle, or end by the sensor. The is achieved by a clear
leader at the beginning and end of the tape. The microcontroller will detect a
problem if the sensors do not detect the light or LED (middle of tape)
and the carriage assembly is up (no tape loaded). The VCR will shut down.
Without a service manual, determining the correct relationships for all
gears may be impossible, but if only one has slipped you may be able to
locate timing marks near the edges of the gears which should line up -
usually when the tape is unloaded. (portions from michael@marconi.nsc.com)
The dew sensor is intended to prevent operation of the tape transport if
the humidity is so high that moisture would build up and cause the video
tape to stick to the rotating drum and damage the heads or get hopeless
tangled as a result.
First, perhaps the dew warning is telling the truth. If you have just
moved the VCR from a cold area to a warm one, let it sit for an hour or
so and see if the dew warning goes away. If you just fished it out of
the toilet or scraped stewed peaches from the interior, well, dew may
be the least of your problems. Or, if you have just cleaned the inside of
the VCR (or maybe even the outside if you were really overzealous!), some of
the liquid may have gotten on the dew sensor (it is likely to be near the
video head drum) so waiting a few minutes may be all that is needed to
rectify the situation.
Assuming that there is no reason for a dew warning, the dew sensor
may be bad or have changed value. There may or may not be an adjustment
for this.
Before you go inside, try unplugging the VCR to clear any spontaneous
fault condition - see the section: VCR has gone
whacko.
The dew sensor is a resistor that changes value when there is condensation.
If the sensor is bad, you should be able to replace it with a resistor and
keep the VCR happy. You should be able to determine the appropriate
resistance by trial and error. If it is the type where the resistance
decreases with moisture and the controller does not care if the resistance
is too high, then you can just remove it. Either way, you have now lost
the protection that the dew sensor provides. Replacement is obviously best.
Don't overlook the possibility of a bad connection - it may be plugged
in and just need to be reseated.
One type looks like a ceramic board, maybe 1/4" - 1/2" on a side with a
silver/gray printed circuit pattern.
If the A/D or whatever is used to determine when there is dew is faulty,
then you will most likely need a service manual to troubleshoot it.
Apparently, given the marginal value of the dew protection and the problems
caused by it, newer VCRs may not even have a dew sensor.
The following pair of recommendations would seem to contradict one-another
slightly but could still be a start:
(From: John R. Hepburn (jhepburn@recorder.ca).)
I use a 3.3K... No great technical justification other than 1 to 10K works on
most machines and I ended up with a lot of 3.3K from an auction. Now if I
could just get about 10,000 more old VCRs with a flashing dew light I could
get rid of this darn box!!!
(From: Dan Sofie (sofie@olypen.com).)
The problem may not be the dew sensor but the support circuitry instead. In
most circuit designs with dew sensors, it is ON (moisture detected) at about
450 ohms or higher and it is OFF (dry) at about 450 ohms or less. Try
bridging a 100 ohm resistor across the terminals to see if the light goes out.
If not, the problem is not the dew sensor, but the circuitry it interfaces
with.
This may mean that the VCR has somehow been programmed to prevent use
by unauthorized kids (you are not reading this if you are a kid, right?)
Even if your model does not have this feature, the same basic chassis is
probably used for a range of models so it could have gotten into a
confused state.
I don't know what kind of recourse you may have as an unsatisfied
consumer, but I would try to get some resolution through your place of
purchase. Such a VCR has all the symptoms of Alzheimer's disease - it should
not be failing in these ways so early in life unless it is under penalty
of hard labor in the damp snake infested dungeon of an English castle! Or
it has been the depository for peanut-butter-and-jelly sandwiches, applesauce,
or marbles!
All the usual recommendations of cleaning and checking rubber parts and so
forth apply to units that have seen significant use or are a few years old
or both. Something this new under normal use should not be causing this
amount of grief. However, sometime I wonder whether using a machine very
little contributes to problems.
First try your place of purchase - there may still be some degree of
interest in maintaining customer satisfaction.
If you have given up on the store, start by checking the rubber parts for dust
and deterioration (with that kind of use, dirt should not be a problem,
but dust or smoke can accumulate), check for adequate lubrication (but don't
add any unless it is definitely needed and then only the smallest amount -
VCRs do not need much oil or grease and too much will just compound
your problems - and check for foreign objects especially if there are
small kids about.
While these could be symptoms of a actual problem, first try unplugging the
VCR from the wall outlet (don't just turn it off) for a minute or so.
If this does not help, try unplugging for a couple of hours - this will
usually drain the backup battery and reset many other functions of the VCR.
If one of these techniques results in the universe returning to normal,
there may have been a power surge or lightning strike nearby
which threw the microcontroller into a confused state. It may never happen
again. However, power surges can be the result of heavy appliances like
air conditioners on the same circuit. If this is the case, you should
consider using a different circuit for your electronic equipment.
If this behavior started when the VCR was just plugged in or following
some other action requiring the mechanism to move or initialize, check for
mechanical problems like a broken belt or one that has popped off its
pulleys or an obstruction like a rock or toy that is preventing the VCR
from completing the required motions. Also see the section:
VCR is failing the power-up sequence.
Once you have ruled out mechanical problems, it is likely that the VCR
has a microcontroller, power supply, or other electronic problem which
may require professional service.
The clock and programming backup may be a supercap - a very high value
special electrolytic capacitor - as much a 1 F (1,000,000 uF) at 5-12 V.
Alternatively, it may use a rechargeable NiCd battery. In either case,
these are easily replaceable with standard parts. A NiCd battery pack of
similar ratings should be readily available. Supercaps are available from
large electronics distributors.
NiCd batteries fail in two ways - loss of capacity or shorted cells. If
memory is retained for a much shorter time than it used to, then the battery
has probably lost most of its capacity. If you measure less than n x 1.2 V
for an n cell NiCd battery pack after it has been charging for awhile,
there is likely a shorted cell. In either case, the best solution is a
replacement though the various common techniques for rejuvenating NiCd
battery packs can be attempted (remove from VCR first!).
The non-volatile memory could use a special chip like EEPROM which does not
require power or a battery backed SRAM or be internal to one of the
VCR's microcontrollers. Channel memory may use a separate power source
from the clock and programming, possibly a Lithium battery since it is
undesirable for the channel settings to be forgotten even if the VCR is
unplugged for a month or more as it is such a pain to reinitialize them.
Rechargeable batteries have too high a self discharge rate.
See the section: Display is dead but everything
else works for more information.
Note that as a preventive measure, if your VCR has a dimming feature, use it.
Operating the displays at lower brightness will prolong its life.
CAUTION: Try the following at your own risk - too much voltage on the
filament will melt it.
(From: John Robertson (jrr@flippers.com).)
If these are the blue fluorescent displays then they might be able to
be recharged. A bit of background first - a number of years ago people
were finding that the blue fluorescent displays in Gottlieb pinball
games would dim over the years until they were unusable. One clever
fellow discovered that if you heated the filaments in these tubes
until they glowed a dull red, by increasing the filament voltage, then
the tube would work again at almost it's original brightness, plus
this "recharge" would last for years in many cases. The normal
filament voltage for some of these displays was in the order of 4 VAC
and if the filament was then run at about 8 to 12 V (dull red to medium
orange glow) for about ten seconds that the job was done.
So, if these tubes have a filament (several very fine horizontal wires
inside between the front glass of the tube and the digit plane) - the
connections would be the very first and the final pin of the tube,
check the voltage there (AC or DC?) and then with the device turned of
and a variable voltage source try increasing the filament voltage
until you see the glow, then try the display out in normal operation.
(From: Andy Cuffe (baltimora@psu.edu).)
I've also had some success with increasing the negative bias to the
filament by a few volts. I have an NEC VCR that had a very dim display
even after replacing the bad caps in the power supply. Changing a zener
diode to increase the negative bias by about 5 V did wonders.
The VFD is usually designed to operate in a multiplexed mode to minimize pins
and drivers at the expense of more complex logic - but that is all inside the
system controller chip anyhow. Thus, there are 'segments' which correspond to
the portions of each character and individual symbols, and 'grids' which are
in effect, enables for each character or group of symbols. Compared to a
multiplexed LED display, the segments correspond to rows and the 'grids' to
columns. The filament, grid, and anodes operate in the same manner as in a
vacuum tube (valve for those on the other side of the lake) or a CRT, for that
matter. A typical VFD might have 9 segments and 7 grids for a total of 63
possible individually controlled displayed items.
The filament requires 2 to 6 VAC. Each of the segment lines are sequentially
pulsed to about 30 V or more while the appropriate set of grids are pulsed
positive to enable the desired combination of displayed items.
Here is the pinout for a typical VFD (from a Sharp VCR):
All other pins are either not present or no-connects. While specific pinouts
for each VFD device are likely to differ somewhat, the general arrangement
appears to be similar - filaments on the ends, grids mostly on the low
numbered pins, a gap with no pins or unconnected pins, then the segments on
the high numbered pins.
Remove the front panel and with the VCR plugged in, turn out the lights and
inspect the filament, several very fine wires running the length of the
display. They should be glowing a very faint red-orange. If you see nothing,
the filament voltage is likely missing. Filament voltage may come directly
from the power transformer (if a non-switching type power supply) or be one
of the DC outputs of the supply.
Check around the VFD for the +30 VDC (approximately) or if you have a scope,
look for pulses on the pins of the VFD. If the +30 VDC is missing, there will
be nothing displayed. In some VCRs like those manufactured by Hitachi, a
separate DC-DC converter module provides power for the display only. See the
section: Dead clock in Hitachi manufactured VCR.
Look for bad connections, open resistors, blown IC protectors or fuses, etc.
Of course, if the VCR has an on-screen display, you will be no worse off than
many newer models that have done away with the front panel VFD entirely!
(From: Paul Grohe (grohe@galaxy.nsc.com).)
The fluorescent display in the VCR's I have seen require three sets of
voltages:
The DC-DC converter usually provides a "floating" 3 VAC winding, a
low current -12 VDC tap connected to one of the filament leads,
and a +20 VDC to +30 VDC segment drive voltage.
If you look really, really closely at the display, you will see
the faintly glowing filaments stretching across the length of the
display.
It figures that the makers of VFD's would have a nice section on VFD displays.
Here are some links to appnotes for driving VF displays. They have a few
"tidbits" in them. AN-440 has a nice graphical depiction on page 2.
(From: Mark Zenier (mzenier@netcom.com).)
A DC filament supply can cause a brightness variation across the display
depending on the design. And, as I remember it, some of them have lower
filament voltages, like 2.5 VAC. A fatal thing to burn out.
The only one I've really messed with was a 32 character, 14 segment
character display. It used a 6 volt filament, and 60 volts on the grids
and segments/anodes. The filament/cathode was biased 6-9 volts positive,
so that when the grids were grounded, they were negative relative to
the cathode.
The power supply for this display was rather quirky, it used a H-bridge
with emitter followers supplied by the system 12 volts, but the lower
drivers of the H were clamped at 6 volts so that it supplied 6 vrms at
a high (5-10 kHz) frequency to the filament, offset by the 9 volts,
and a transformer, hooked up differentially, stepped that up to the 60
volts for the drivers. A real RFI pain in the ass.
To confirm that it is your VCR doing the dastardly deed, play or record for
at least a minute on a tape known to be in good condition. The use REV to
back of the tape for about 15 seconds. Eject and open the cassette door by
releasing the latch and inspect for edge crinkling.
Any rippling along either edge of the tape is an symptom of a possible
problem. It isn't only that the tape does not make good contact
with the audio or control head (depending on which edge is damaged)
but just an indication that the tape may not be moving through the
transport precisely positioned.
Assuming you are having the same problem on multiple tapes and that
using a known good (new) tape results in damage:
This is an indication that your tape path alignment is off or your rubber
parts (probably the pinch roller) need replacing. The tape is wandering
up and down as a result of unequal pull from the capstan due to a glazed/worn
pinch roller. There could also be other aspects of tape path alignment like
roller guide tilt (which is probably not adjustable), A/C head tilt, dirt,
roller guide height (don't mess with it), etc. See the chapter: "Tape Path
Alignment and Backtension Adjustment. It could also be worn feet on the
roller guide assemblies causing the guides to not be perfectly vertical.
Replacement of these parts may be the only cure. Other much less likely
possibilities: excessive or varying backtension, tight idler clutch,
electronic problems.
For a VCR with very high mileage, it is also possible that there has been a
ridge worn in the surface of the control head preventing consistent contact
between it and the tape:
(From: Phil Reed (100555.244@compuserve.com).)
Other related symptoms include:
If you look carefully, you should be able to see the tape wandering
slightly producing the muddy sound and erratic tracking. The tape
may not be perfectly smooth in passing over the various guides and rollers.
Normally, you will almost not be able to tell the tape is moving at
all except by examining the reel rotation - it is that mirror smooth.
First, clean the tape path properly, especially the capstan and pinch roller,
tape guides, A/C head. Inspect the pinch roller for glazing, cracking,
etc. and replace if necessary. See the sections: "General guide to VCR
cleaning and rubber parts replacement" and if necessary, the chapter: "Tape
Path Alignment and Backtension Adjustment".
Another possibility is that the control portion of the A/C head stack is dirty
or defective or there are problems in the wiring or its circuitry. Double
check that the tape is in solid contact with the bottom of the A/C head stack
(where the control track is located), that the head is clean, its connector is
clean and seated properly, and look for any broken wires or bad connections.
On a VCR with autotracking, the autotracking light may be flickering as well.
Possible causes for loss of lock:
Inspect the tape path really really carefully to determine if there is some
obstruction preventing tape-control head contact or other mechanical problems.
Try cleaning the tape path and checking the rubber parts. Check power supply
voltages if you can determine what they should be (see the section:
VCR power supplies. If these procedures to not
reveal anything amiss, you will need a service manual to pursue electronic
faults.
When the bottom of the tape gets creased, the control head may no longer
align with the control track and you loose servo lock on the sync signal.
Your audio may be fluctuating in intensity as well since the audio track
is wandering also and the tape may be intermittently going in and out of
correct tracking and/or changing speeds. Since the tape can no longer
seat stably on the lower drum guide ridge, there could be other problems
such as noise bars along the top or bottom of the picture, jumping, etc.
It could be the guide posts or other tape path components, but before you turn
every screw you can find and make the problems hopelessly worse, replace all
of the rubber parts - belts, idler tire, pinch roller. And while you are at
it, give the machine a good cleaning.
A dirty, worn, hard, dried out pinch roller in particular can result in
the tape wandering up and down causing tracking problems and creasing the
tape in the process. This is probably the most common cause of tape damage
assuming the VCR itself has not been abused (i.e., jammed cassette removed
using a pair of Vice-Grips(tm).)
With a thorough cleaning of everything before buying the new rubber (which BTW
should not be more than a total $10 to $15 from a place like MCM Electronics),
you may at least see a temporary improvement in performance - and confirmation
of the diagnosis.
You really need to determine exactly where the tape is being creased.
Once you do this, you may be able to determine the cause and visually
verify whether the problem is affected by any of your adjustments or probing.
Some other possibilities include:
(From: Raymond Carlsen (rrcc@u.washington.edu).)
There is a simple way to determine if the tape is skewing or has a tendency
to do so... just reduce the back-tension by holding the arm so the tape is
not as tight around the drum. If there is any tendency of a worn pinch
roller to skew the tape, that will show it up quickly. I make my test tapes
on an old linear stereo VCR and record two different tones on the two audio
channels. When I play that tape back on a VCR with linear mono audio (all
of them now), the two tones will play with equal volume if the audio head
height is correct AND the tape is not skewing up or down. I can determine
what's happening by ear, without even looking at the tape, and before the
tape is damaged. Note: there are some machines that tend to skew even if
the pinch roller is good. Those require more aggressive alignment
procedures than the service manuals usually supply. Almost everything on
the take-up side of the tape path can be "adjusted" for the really stubborn
ones (even shims to tilt the capstan rotor), but in a few cases, there is
just no way to get it perfect. With machines getting cheaper and cheaper, I
don't spend any time on dogs unless it's a high end deck and the customer
knows what it's worth.
(From: Vern (vgdeuel@ticnet.com).)
Tape damage along the top edge usually indicates too much back tension
which, among other things, can be caused by the P2 roller not turning
freely. Using a Tentelometer, check the back tension at the full erase
head; it should be about 30 grams. Then check the tape tension just
before the A/C head. If it's up around 80-100 grams or so, change the
P2 roller and even the P3.
(From: Jerry G. (jerryg50@hotmail.com).)
Take a careful look at the capstan shaft and see if the capstan (where the
pinch roller touches) is very clean. If it has black or brown markings
(coating) on it, you must clean it off very well. Use alcohol and a Q-Tip.
Take care to not scratch the shaft.
If the rubber pinch roller is shiny, or looks dried out and or cracked, change
it. This area other than the reels is a prime cause of speed problems. The
tape when under normal torque can be slipping between the pinch roller and the
capstan shaft.
Some VCRs also have other timed modes - sort of like the timed off function
of a clock radio. Pressing the 'Off-T' button adds time to record or play
in 15 minute increments and then the VCR shuts off.
For real-time counters, this may mean a problem deep in the electronics
requiring a service manual. However, if you are attempting to play a tape
that has nothing on it, the real-time counter will not change. This is
normal as there are no control pulses on the tape.
For non-real-time counters, if the display skips counts or 'free runs' -
counts very quickly at certain times, this could be due to a defective
sensor or hysteresis circuit. If it counts in the wrong direction, a logic
problem is indicated as direction is determined by the microcontroller being
aware of what mode the VCR is in - there is likely no actual direction
sensing on the reel.
See the section: A HREF="#vcrrrotstst">Reel rotation sensor testing
for further information.
Sometimes, when snow or serious video noise suddenly occurs while playing a
rental, old, or damaged tape, it means the video heads have picked up some
oxide and are no longer making good contact with the tape. Letting the VCR
play a newer tape for a few minutes may clear this if it is minor. However,
video head cleaning (using a cleaning tape or the manual procedure described
in the section: Video head cleaning technique)
will probably be needed. But, first start with the section:
Snow on one or more speeds and NEVER NEVER attempt
to clean the video heads without using one of the recommended techniques -
you can easily destroy the heart of your VCR! Also, never attempt to play
or record on a spliced or seriously damaged tape as this can also result
in destruction of the video heads.
This may mean that the record protect tab on the cassette is broken off or
the record tab sense switch is dirty or bad.
This could be the result of a dirty or defective record sense switch or
misalignment preventing proper engagement with it. Some VCRs check for the
record tab constantly while others just check when the REC button is pressed
or the timer initiates record.
It could also be a defective reel or tape end sensor halting record though
these would likely affect playback as well.
This means that the old recording is being erased (if there was one) but
nothing or too weak a signal is being written by the video heads.
This could be due to a variety of electronic faults as well as marginal or
bad video heads.
This is normal at the start of a recording made on top of an old recording
if your VCR does not have a flying erase head. However, it should wipe down
the screen in a few seconds and disappear.
If it does not go away, then your full width erase head is not working.
This could mean that one of the two heads used for record is dirty or
defective.
The audio dub switch (if any) may be in the wrong position or the audio
circuitry may be defective.
This likely means that you are attempting to record (copy) a Macrovision(tm)
or some other copy-protected tape or your cable or satellite company is
transmitting copy-protected video.
Info on Macrovision can be found at:
Some of the new digital DBS satellite receivers output a Macrovision copy
protected TV signal so you can't tape the movies from them either.
Newer VCRs will generally not record successfully. Some older VCRs will
record without problems. See the section: Why VCRs
will not copy (Macrovision) copy protected tapes. (8mm VCRs may record
the entire signal and therefore be able to playback successfully. However,
attempting to copy the 8mm tape onto a VHS tape will result in the same
problem.)
For 2 head VCRs:
For 4 (or more) head VCRs:
If this VCR has 4 or more heads, SP and EP may use a different set of heads,
so certain heads may still be dirty or bad. If the machine tracks
perfectly in EP, then alignment is probably fine - EP is more critical as
to alignment as the EP track is 1/3 the width of the SP track.
Have the video heads been cleaned using the proper procedure (not just a
cleaning tape - see the section: Video head cleaning
technique).
New video heads may fix this, though it can be caused by other problems such
as weak read electronics. See the chapter: "Video Heads and Upper Cylinders".
You should also check the backtension adjustment - if too loose, head to
tape contact will be compromised. Try increasing it momentarily by pushing
the backtension lever slightly to the left while the tape is playing. The
usual way to adjust backtension without a backtension meter and service
manual is to look at the image just before vertical retrace at the bottom
of the screen - this is normally not visible unless you can reduce vertical
size or play with vertical hold to get the vertical blanking bar to appear.
Of course, most modern TVs don't have any such controls! This is the head
switching point and when the backtension is properly set the image above and
the bit of image below this break will be approximately aligned.
If increasing backtension helps, either the heads are marginal or the back-
tension was low. However, low backtension will usually show up as a waving
or flagging effect at the top of the picture.
OK, well, if it is indeed your most watched tape, THAT may be the cause
(especially if it happens during the same scene!) or it may be a problem with
the VCR:
The most likely cause if you rent movies or have a collection of older well
used tapes is the first - your tapes are bad.
If a prerecorded tape that plays properly on another VCR, shows the effect on
the suspect VCR - AND - then shows the same thing on the other VCR, it is
being damaged by something in the tape path.
Open the door of the cassette by releasing the catch on the side. Look
carefully at the surface of the tape - it should be mirror smooth all
across. If you see any evidence of hair fine (or larger) scratches running
the length of the tape these are what are causing the line. This is likely a
result of a bit of debris or a rough edge on one of the guide posts in the VCR.
The effect on the picture is opposite of the vertical location on the tape -
lines near the top of the tape affect the bottom of the picture and
vice-versa.
Get a brand new tape or a known good tape (that you can afford to mess up)
and test it on another VCR (at the tape speed that is worst, if this matters).
Assuming playback is fine, play it on the suspect VCR for a couple of minutes.
Pull the plug (DON'T hit STOP) so the transport remains in the fully loaded
position. Now, carefully examine the surface of the tape all along the tape
path (disturbing its position as little as possible) to identify the location
where the damage begins. It may just be a bit of something stuck to a guide
post. Has the VCR been cleaned in the last 10 years?
Note: This sort of damage to the tape does not represent a risk to your VCR's
video heads so you can continue to use the tape if desired.
This is probably a mechanical problem, most likely an adjustment or fault
related to tape path alignment. However, it could also be due to
electronic problems with the video or servo circuitry. The vertical sync
could be corrupted or the head switching point not set correctly.
The head switching point is 6.5 lines before vertical sync. If this ends
up moving into vertical sync for some reason, you will get unstable
video. The supply side roller guide height adjustment is also critical and
would be the first thing to check mechanical alignment problems are suspected.
However, don't overlook the obvious: your TV is marginal or misadjusted
or you are attempting to play a bad tape.
VCRs with 4 or more heads will usually have a V-Lock adjustment - either a
knob on the front or rear panel, or sometimes 'conveniently' accessible from
under the VCR. Sometimes, a special tool is needed to adjust this control.
Where tracking is adjusted with a set of +/- buttons, these may also be used
in PAUSE mode. There may be separate adjustments for SP and EP(SLP) speeds as
well. In any case, these settings are made while viewing a tape recorded
at the appropriate speed in PAUSE mode.
For LP speed - which is being phased out by many manufacturers, at least
for record - these special effects usually do not work well if at all.
This is basically due to the nature of the sync signal alignment on tapes
recorded at LP speed and would require complex circuitry to handle properly
at anything other than normal LP play speed. (If you care, the sync tips
between adjacent tracks align on the tape in SP and EP recorded tapes but
are off by 1/2 line with LP recorded tapes. This results in the tearing
seen in search modes with LP recorded tapes.) Since this tape speed is of
little true value - it is a compromise anyhow - the added expense has been
found not to be justified except on professional machines.
Most 2 head VCRs will work fairly well on EP recordings but show noise bars
over about 50 percent of the picture with SP recordings. For those made at
LP speed, tearing will occur in addition to noise bars if they sync at all.
Few VCRs deal properly with LP search as substantial additional circuitry is
required.
In my opinion (IMO), any picture is better than a blank screen or no search
capability.
I also noticed that if I have the tape counter displayed on the screen, and
when the counter progresses its count, the tape plays properly. Then all of
a sudden the counter stops counting and the problem continues again.
I have cleaned heads well, cleaned tape path, and even cleaned the underside
of the takeup reel, all to no avail?"
First, make sure the tapes are in good condition. They may have been damaged
(edge crinkled) before you serviced the VCR. This is now causing your erratic
behavior and there is nothing wrong with the VCR.
Before considering drastic action, record on a brand new tape - from end-to-end
if the initial results seem promising. You may have a non-problem.
Try recording you your VCR and playing back on another one. If this works,
then bad tapes are the most likely explanation.
If this does not work, there could be electronic problems:
(From: Stephen Isaacs (stephen@myna.com).)
The normal playback of a pre-recorded tape suggests most things are working
fine. The self recorded problems point to a faulty control track recording
system. bad oscillator, or amp. It is also possible the erase head is not
doing its job making it difficult to record a new control track over an old
one.
(From: Richard (vcrtips@mail.vii.com).)
Almost all pre-recorded tapes are recorded at the SP speed.
If you are like most people, you probably do your recordings
at the EP speed (to get as much on the tape as possible). Do
you have the same problem if you record at SP? Your VCR
probably uses different heads for SP and EP. You may have
dirty EP heads, defective EP heads, a head amp problem. Or,
there could be a tape tension or other mechanical problem.
(From: Frank D. Ralston (fdr@continet.com).)
Check the following:
The rotational position reference for the video head drum is usually
supplied by a pickup in close proximity to the edge of the lower
cylinder (probably) which has a small magnet fastened to it.
This generates the so called 'PG' pulse and is used by the servo
circuitry to properly control the drum rotation and the head switching point.
If this sensor is moved or if there is a fault in the PG circuitry, a
variety of record or playback problems can result. Without this reference,
the servo circuitry has no way of knowing where the A and B heads are
at any given time. During record, this may result in recording video
which is not properly lined up with the video tape - a track may consist
of the end of one field and the beginning of the next rather than an
entire fields as it should. During playback, the head switching point
may occur at the wrong time resulting in a partially snowy or missing
picture since a head that is not even in contact with the tape may
be active. Similar problems may make look like your TV's vertical
hold control is set incorrectly with the vertical blanking bar visible
at an arbitrary point on the screen.
The assembly on which the rotating magnet(s) are mounted and the upper
cylinder may be secured with one or two set screws. If these loosen, the
the precise relationship may be lost resulting in a shifted head switching
point. It may even be random - changing location each time the drum starts
up due to the inertia of the upper cylinder. If this is the case, you will
need a service manual to properly adjust the angular location of the magnet
assembly unless there are obvious 'timing' marks to guide you.
Beyond confirming that the pickup coil is in close proximity to the drum,
the rotating magnet and sensor are secure, and that there are no bad
connections or loose connectors, there is not much to be done for these
problems without a service manual.
The definitions below are just For Your Information (FYI):
This effect will not occur (except possibly at the very beginning of the
tape) as long as you record from start to end without backing up the tape
at any time.
If the rainbow pattern is present whenever recording over previously
recorded tapes and does not go away, then your full width erase head
is not working. This could be due to an electronic failure or simply a bad
connection to the full width erase head. Alternatively, a mechanical
problem such as a broken or popped spring or gummed up lubrication might
prevent the pivoting full width erase head from contacting the tape properly.
This is likely an electrical fault in the chroma playback circuitry buried
deep in the bowels of your VCR. The chroma reference is not locking or is
locking erratically with the chroma signal. Unless you can find some bad
connections or other obvious problem, this will be difficult to troubleshoot
without schematics. Don't be tempted to twiddle internal controls even if
they appear to deal with color - you will just mess things up for whoever
finally repairs your VCR!
First, if this wasn't the original complaint, make sure the flag waving
problem exists with the TV that will actually be used with the VCR - it
may just be your test TV or monitor that is unhappy. If the problem
does exist on the relevant TV, all modern TVs have a dedicated video channel
button(usually channel 0) which has a shorter flywheel line-timing duration
allowing the TV timebase to lock up more effectively to unstable video
sources such as VCRs. It may be that simple.
(Parts of the following from: Andrew Morphitis, Andrew@andrewsm.demon.co.uk).
This fault is sometimes known as flag-waving when associated with video
recorders. If the tape back-tension provided by the tension arm and
supply reel-table is not the same as the back-tension provided when the
tape was recorded (possibly on another machine) then the field timing of
the video tracks being played back will be inconsistent . Your back-
tension can be checked using a back-tension cassette gauge (a typical
reading would be about 35g-cm for VHS) or you could adjust the back
tension using a known good test tape (or reliable pre-recorded tape)
until the waving disappears. If your back-tension does turn out to be
incorrect and you adjust it according to the manufacturers spec. then
all of the tapes you have previously recorded will probably still
exhibit this waving problem - adjust to spec. or to your tape library -
take your pick.
That's the theory - now the practice. Back-tension refers to the tension
of the tape over the head drum, this is provided by the felt covered
metal band (tension band) which is wrapped around the supply reel
(left-hand reel from the front), the friction providing the tension.
There are usually two adjustments associated with back tension and these
can be found near the opposite ends of of this tension band, the tension
arm operating position and the anchor point of the band. Adjusting the
latter position will increase or decrease back tension (you will want
to increase your back tension which has dropped due to excessive wear
on the belt). If you do give it a bash then be aware that poorly
adjusted back-tension can, at worst, give rise to premature head wear.
Because of the differences between the back tensions of different
machines, all modern TV's have a dedicated video channel button
(usually channel 0) which has a shorter flywheel line-timing duration
allowing the TV timebase to lock up more effectively to unstable video
sources such as video machines. Are you using the video channel? - try
playing the video through different channels on your TV.
The head fault used to be specified +/- 10 us, then it became 16 us, 20 us and
I think we have already seen 22 us. Sooner or later a TV will not be able to
follow such large phase jumps before the picture begins. Some TVs can be
modified and some can not. The problem is that the line deflection circuit CAN
NOT instantly follow a large phase jump, the output transistor would be
destroyed at once. It HAS to be distributed over a certain number of
lines. You can only hope to distribute the phase jump evenly over as few lines
as possible and that there is neither overshoot nor tail to the
response. YMMV.
It is logical to see more problems on old tapes or on tapes that were recorded
on another machine (especially rental tapes) because the phase jump has
everything to do with mechanical tolerances and tape stretch. It should be
much better on a new tape that has been recorded on your (his) new machine.
Macrovision anti-copy protection only makes matters worse !
I think I will buy me a nice new JVC S-VHS machine with built-in timebase
corrector. Also, our new European Philips chassis has an input IC with
built-in timebase corrector. That should help a lot.
If this VCR also will not record audio, see the section:
No (non-HiFi) sound on new recordings.
The following assumes this only happens when playing tapes:
While playing one that you know has good audio, carefully touch each of the
terminals of the A/C head with the tip of a small screwdriver - if the audio
circuits are working, the audio head terminal should produce a buzz from the
speaker. CAUTION: Insulate all except the tip of the screwdriver to prevent
shorts.
Other possible causes: Debris or problem with tape path alignment causing
loss of contact with audio head in vicinity of audio tracks, bad audio head
(but this would probably result in inability to record audio as well).
Make sure your tape isn't bad. Yes, I know, this is unlikely, but very
old tapes tend to lose oxide along the edges and that's where the linear
audio goes.
If the previous audio is erased but you now have silence, the problem could
be that erase is working but no new audio is being recorded on the tape.
First, check any audio mode or dubbing switches for proper settings.
If you are using the RF input, see if the same problem exists with
the RCA inputs. Sometimes, dirt/bad connections on the RCA inputs will
trick the VCR into thinking you really want to use those instead of the
RF. Pushing an RCA plug in and out a few times may clean these off.
If you are using the RCA inputs, make sure the the audio cable is plugged into
the proper jack on the VCR and that there is audio from the source (plug
it into an amplifier or another VCR to test).
(From: Raymond Carlsen (rrcc@u.washington.edu).)
I first saw this problem in Wards (Sharp) VCRs, then later in some
Samsungs. The real problem is a bit of resistance in the connector on
the full erase head. The FE head arm swings back and forth when
loading and unloading the tape, causing the connections to weaken.
That bit of resistance cause the bias/erase oscillator to fail to
start up in record mode. If allowed to run that way, it can burn up
that transistor and other components on the audio board. Just
replacing the bad parts will not fix it for long. Cut off the plug and
direct-solder the full erase head wires directly to the head.
End of problem. Done a bunch of 'em.
How is the TV connected? Through the RF/antenna input? If through the RCA
jacks, of course, it could be a TV/cable problem. Bypass the VCR and check.
For the RF, this could be many things:
If you are getting a mixture of old and new audio, then there could be
a problem with the audio erase head (part of the A/C head stack) or its
circuitry.
Clean the audio/control head (the stationary head to the right of
the video drum near where the tape re-enters the cassette. Check for
dirt or tape oxide on or around the audio/control head.
Beyond this, testing will probably require a schematic. However, if you
can locate the connections to the audio erase head, use an ohmmeter to test
for continuity of the coil. Check with an oscilloscope for the high
frequency erase signal during record.
The sound out of a HiFi (not just stereo) VCR should be virtually
indistinguishable from the original and for good quality source
material, nearly as good as a CD.
What to look for if it is really playing HiFi (try at slowest tape speed
as this will have little effect on HiFi quality but will turn the linear
track quality to crud). Use a tape with a musical recording for this:
However, problems are possible:
Try adjusting the manual video tracking control as this will also affect HiFi
audio tracking and see if this clear up the sound.
Like video, recording HiFi audio needs to use the heads twice. Thus, a
slight loss in sensitivity or frequency response may still enable
pre-recorded tapes to work reasonably well but will result in problems of
playing back self-recorded tapes. Note that slight tape path misalignment
would not affect self-recorded tapes anyhow but would result in poor
playback of others - the opposite effect.
Note that A/C height doesn't change on its own - someone has likely been
mucking with your adjustment screws (and who knows what else)!
To confirm, record a couple minutes on a brand new or bulk erased tape. If
the last 5 to 10 seconds of the recording is clear, the A/C head alignment
is at fault since it is writing over the ends of the HiFi tracks 5 to 10
seconds *after* they are laid down and the end of the recorder will be
unaffected.
(From: Jerry ().)
The HiFi heads are more critical than the video heads. If they are warn down
a bit, they can be very instable. Sometimes I can get a bit of a better
response by increasing the tension arm tension a little. If you do this, you
may have to touch up the guides.
(From: Anthony Falvo (afalvo@borg.com).)
I have had good luck making the HiFi tracking point meet the video head
tracking point with slight adjustment of the 30 Hz switch point.
The noise you are hearing is FM audio track switching noise - from the
changeover between the hi-fi audio heads on the head cylinder. The difference
between video and audio switching noise is that the video noise can be shoved
out of sight in the vertical blanking interval. The trouble with the audio is
that our ears listen all the time! Some VCR's exhibit this worse than others.
You can try adjusting the switching point to minimize it, but by the same
token, some precorded tapes are particularly bad, with Disney tapes being
about the worst I have ever heard.
(From: (Parker C. (parkerc@halcyon.com).)
Your hifi audio is, technically speaking, not fluttering. The distortion
you hear is the head switching noise becoming audible as the hifi heads
are wearing out.
On the outside chance you are not dealing with a worn out upper drum, you
should first check the video envelope and confirm that your machine is
mechanically adjusted correctly - i.e. check that the drum guides have not
slipped. Hifi audio would typically become distorted if the tape path is
not adjusted correctly. Audio playback level will not help the situation.
Hifi Record levels almost never need to be adjusted, unless someone has
been tweaking them in the field. (hint, hint).
A note on record levels: occasionally we find that decreasing the video
record levels on machines with poor hifi audio recordings will quiet
things down for a little while. Did everyone get that? (decreases the
video penetration into the hifi region of the tape).
The most common cause for a squealing noise are tired weak belts that are
slipping. Less likely is the need for lubrication.
See the appropriate sections on cleaning, rubber parts replacement, and
lubrication.
Note that A/C height doesn't change on its own - someone has likely been
mucking with your adjustment screws (and who knows what else)!
There is usually a metal strip with a carbon contact pressing against the
center of the video drum spindle either above or below the deck. In rare
instances, the brush may be BETWEEN the upper and lower cylinders requiring
more disassembly. It is very common for it to vibrate is just the right way
to sound like a cat being strangled. Gently press on this strip or lift it
off of the spindle while you hear the sound. If the whine disappears,
cleaning and slight repositioning of the strip should be all you need to do.
Do not remove this strip - it is needed to ground the rotating drum to prevent
static buildup and video noise problems (see the section:
Firing (static) lines in picture during playback.
Note: You may find that if you measure the resistance between the brush to
the chassis that it is far from 0 ohms - perhaps in the 10s or 100s of K or
higher. This is perfectly normal (as long as it isn't infinity!) as static
doesn't take much current flow to be eliminated.
(Portions from: David R Mulligan (skipper@interlog.com).)
It sounds like you are recording the SAP audio channel on the mono audio track,
but normal on the HI-FI track. This would indicate that your television
station broadcasts a Spanish dub over the SAP channel for those who prefer
that language.
Check the position of the audio playback source select. Also, any problem with
the HiFi record or playback would also result in the VCR defaulting back to
linear track playback.
If you can play pre-recorded tapes in color but tapes recorded on this VCR
do not play back in color, there may be several possible causes. The
simplest is that your input signal is too weak - a misadjusted antenna or
cable with a large number of splitters - and the VCR's color killer thinks
there is no color. Sometimes the threshold for detecting the color signal is
set higher on the VCR than the TV which you are using to monitor the
recording.
Some questions:
If the answer to all but the last question is 'yes', then the problem is most
likely in the video/chroma circuitry associated with recording function. It
could be as simple as the color killer setting being too low.
Possible sources of problems with color recording:
If recording works fine as indicated by tapes made on this VCR playing
fine on another one but pre-recorded tapes do not play back in color and
the VCR works fine in all other respects there could be several possible
causes:
Note that in all cases of missing color, checking with another TV and/or
adjusting the TV's controls should be tried first as slight differences
in signal levels between tuner and playback may cause a TV with marginal
settings (fine tuning, color killer, chroma circuits) to switch unexpectedly
between color and B/W.
Verify that the direct video output (RCA jacks) works properly with a
pre-recorded tape. If this is noisy as well, then there are problems
with the video circuitry or video heads.
If there are problems with the Channel 3/4 output but the direct video
outputs are fine, then suspect a weak or dead RF modulator. This is
a little metal metal box with the Antenna In and TV Out connectors.
It has circuitry which switches between the VCR's internal video
signal and the antenna input. It also converts the video baseband
signal to the channel 3/4 output required by the TV.
Before you conclude that the RF modulator is to blame, check that the channel
and fine tuning of the TV are properly set and that there are no other
problems with the TV. Test the VCR with another TV. It could be that
the signal from the VCR is just a little weaker than it is used to be.
Try moving the channel 3/4 switch back an forth - it may have developed a
bad contact. Try the other channel (3 or 4) - it may work better. Try
moving the VCR away from the TV - sometimes interference from the TV will
degrade the video quality.
If you do conclude that the RF modulator is at fault, generic
replacements are available from the parts sources listed near
the end of this document or other electronics distributors for less than
$25. Replacement is straightforward since there are only a couple of
soldered connections but getting to the unit physically is sometimes a
challenge.
If the signal is preset into the VCR, there still may be a bad connection
inside preventing it from making it to the VCR's tuner. Sometimes, there
are RCA style plugs inside that work loose.
Otherwise, the tuner of the VCR is not working. This could be because it
is broken or power to it is bad or missing. If all other functions
of the VCR are working, it is likely (though not guaranteed) that the
power supply is fine. There could be bad connections or dirty connectors
as well.
Beyond probing for bad connections and verifying your antenna hookup, there
is not much that can be done without a service manual and test equipment.
If the problem is that it won't tune upper cable channels, that may be by
design. Older VCRs - despite being called 'zillion channel cable ready',
may not be able to deal the upper channels of modern cables systems:
For example, a typical older 110 channel cable ready VCR is able to receive
only these: Cable: 14-36, A to W, 95 to 99, A-5 to A-1, VHF 2 to 13, and UHF
14 to 83. Total: 110 Channels. The only way around this is to get a cable
box capable of receiving all of the channels that your cable company provides
and set your VCR on channel 3 or 4, or buy another VCR that will tune in all
of the cable channels.
Determine if it in the video signal or is it only present when the VCR is
close to or sitting on/under the TV? If so:
One simple test to see if it is the TV doing the interfering is to record
a program partially with the TV off and then with it on - without changing
anything else. If the quality of the recording is noticeably worse with
the TV on, you know what is at least partly to blame.
It is probably interference from the TV's switching power supply, deflection,
or other circuits getting into the low level video circuits of the VCR.
Either the TV or VCR or both are inadequately shielded. Hey, but the makers
saved a few cents!
Is probably isn't the cables but see if moving them around changes anything.
If it does, then better (shielded) cables might help.
It might be worth trying a position a grounded copper sheet between the TV
and the VCR. I don't know how much if at all it will help.
Does it happen when watching from the antenna/cable or only when a tape is
playing or recording?
If you live in an apartment complex - especially newer building of steel
or steel reinforced concrete construction - reception may be inherently
dreadful. Many of these offer a rooftop antenna feed or cable and for good
reason. Try relocating the equipment - sometimes a different part of the
room will have fewer problems.
Did this just start suddenly without you changing *anything*?? Does it now
happen at all times of day?
First, try a different tape - preferably a new recording made on a different
VCR or a new commercial video. It is possible that these streaks are simply
due to dropouts on the tape - missing bits of oxide or dirt causing momentary
loss of video signal. Old, worn, or cheap off-brand tapes are particularly
prone to dropouts.
One characteristic of dropouts is that they may span video lines as well as
video frames. If your lines are very short and random, they may be caused by
a dirty, missing, or improperly positioned video drum static brush. In most
VCRs, you will see a metal strip with a carbon contact pressing against the
center of the video drum spindle either above or below the deck (or in rare
instances, BETWEEN the upper and lower cylinders). The brush is there to
provide electrical contact between the rotating video drum and the stationary
lower cylinder and chassis. This is necessary since the bearings on which the
upper cylinder rotate may not provide adequate contact and any static buildup
caused by the spinning head cylinder rubbing against the tape may discharge
through the bearings resulting in these firing lines. Carefully remove the
static brush and clean the end of the spindle and carbon contact. This may be
all you need to do to remove the static lines from your picture.
(From: Michael James (michaeljjames@biglake.com).)
The following is for a JVC based deck which is often used by Philips. You
need to use GREAT care as this requires removal of the drum motor and it's
mounting. This will affect the switching point which will cause the picture
to roll uncontrollably or to have noise at the bottom of the picture.
Symptom - White dashes across the screen.
Remedy - Very carefully note the position of the drum motor with relation to
the shaft running through the drum assembly. Remove the screws holding the
drum motor. Note the position of the brass bush and loosen the Allan nut
holding it. Remove the video heads and clean the excess grease off of the
static discharge brushes. If the fault persists replace the brush assembly
with a new brush
If you do not feel confident that you can do this take it to a repair shop,
this job should take no longer than 1 hour to complete.
There are always several different voltages used within a VCR - if one
of these dies, some subsystems will work but will not receive the proper
signals from the dead parts. So, nearly any kind of behavior is possible.
Therefore, the first test is to determine, if possible, that the
power supply outputs voltages are correct - both with power off and
power on.
Some power supply problems are caused by power surges. These may result
in a totally dead VCR or in overstress and subsequent failure of various
components. A power strip with a circuit breaker, even with surge protector
is not a reliable protection against power surges especially during lightning
storms. The only sure protection is unplugging electronic equipment during
storms - but then, what would your insurance agent have to do?
Of course, where the VCR is stone dead, check for a blown line or secondary
fuse in the power supply. Occasionally, a fuse will blow due to a power surge
or for no good reason and a new fuse is all that is needed. However, this is
usually not the case and a new fuse will blow immediately. There is a chance
that additional damage may result - proceed cautiously. If the fuse element
is vaporized - black or silver coating on the glass, a short in the power
supply is likely. However, a violent surge on the power line can also result
in such a symptom.
Various subsystems of the VCR may be protected by individual fuses as well.
Sometimes, one of these will blow resulting in a variety of multiple systems
problems but not a totally dead VCR. Look for fuses on the mainboard as well
as the power supply.
IC Protectors (ICPs) may be present on a single chip or small subsection of
a circuit. Most common types are miniature fast acting fuses. Typically,
they come in a black TO92 or rectangular .1"x.3" plastic case with two leads.
Test these like a fuse - an IC protector should be a short if good.
In some cases you may find a PTC (Positive Temperature Coefficient resistor -
resistance increase dramatically due to excessive current heating the element)
type of fuse or IC protector - these are self resetting once the overload has
been removed. However, this also means that testing with power off will show
low resistance even if a fault still exists (unless you test immediately).
Measuring voltage across such a device with power on is one way of identifying
a problem. One common form of this device appears as a little metal metal
sandwich - the two plates are separated by the active material.
VCRs typically use one of four types of power supplies (There are
no doubt others):
First try to identify which type you have. Here are some general comments
for each type:
Start at the line cord - if there is infinite resistance between the
two prongs, there is a problem in the primary side of the transformer.
A fuse may be blown, the transformer primary may be open (or a thermal
fuse under the outer layers of insulation may be blown), or there may be
bad connections between the line cord and the transformer. If this checks
out, there may be a problem on the secondary side - bad rectifiers,
transistors or IC regulators, or bad connections. It is unlikely that the
secondary winding of the transformer itself is bad.
See the document: Notes on the Troubleshooting and
Repair of Audio Equipment and Other Miscellaneous Stuff for more info.
In a supply that is dead - has blown the main fuse - check **all**
semiconductors, capacitors, and resistors as a failure in one may damage
others and just replacing the first one you find that is bad may result in
it just blowing immediately. Fusable (flameproof) resistors (blue or
brown body or boxy ceramic power type) may open up if there was a shorted
switching transistor. Power resistors supplying current for the startup
circuit may open from age. See the document: Notes
on the Troubleshooting and Repair of Small Switchmode Power Supplies
for more detailed information. Correct output voltages can be determined
with some work - tracing the circuit. However, it is usually safe to assume
that there should be at least one around 5 to 6 V output for the logic and
one or more others at 12 V or higher for the motors and other electronics.
Note: The initial test in (1) for power transformer based supplies of
checking between the prongs of the line cord cannot be used with a
switcher - it will likely always read open even if the supply is perfectly
good.
Always check for the possibility of bad solder connections as well.
Ideally, electronic equipment should be unplugged (both AC line and phone
line!) during electrical storms if possible. Modern TVs, VCRs, microwave
ovens, and even stereo equipment is particularly susceptible to lightning and
surge damage because some parts of the circuitry are always alive and therefore
have a connection to the AC line. Telephones, modems, and faxes are directly
connected to the phone lines. Better designs include filtering and surge
suppression components built in. With a near-miss, the only thing that may
happen is for the internal fuse to blow or for the microcontroller to go
bonkers and just require power cycling. There is no possible protection
against a direct strike.
Most VCRs have their own internal surge protection devices like MOVs (Metal
Oxide Varistors) after the fuse. So it is possible that all that is wrong is
that the line fuse has blown. Remove the case (Unplug it first!) and start at
the line cord. If you find a blown fuse, remove it and measure across
the in-board side of fuse holder and the other (should be the neutral) side
of the line. With the power switch off, this reading should be very high.
With the switch on, it may be quite low if the VCR uses a large power
transformer - a typical primary resistance is 15 to 30 ohms.
Some VCRs may be outside this range but if the reading is extremely low, the
power transformer could have a partially or totally shorted primary. If
it is very high (greater than 1 K ohms), then the primary of the power
transformer may be open or there may be blown thermal fuse under the
insulation wrappings of the transformer windings.
If the VCR has a switching power supply, see the document:
Notes on the Troubleshooting and Repair of Small
Switchmode Power Supplies.
If the resistance checks out, replace the fuse and try powering the unit.
There will be 3 possibilities:
Line filters can also be useful if power in you area is noisy or prone
to spikes or dips.
However, keep in mind that most well designed electronic equipment
already includes both surge suppressors like MOVs as well as L-C
line filters. More is not necessarily better but may move the point
of failure to a readily accessible outlet strip rather than the innards
of your equipment if damage occurs.
It is still best to unplug everything if the air raid sirens go off or
you see an elephant wearing thick glasses running through the neighborhood
(or an impending lightning storm). Generally, the backup battery or
supercap will retain the clock and programming information long enough
to ride out a typical storm.
Do all modes 'go out' or just PLAY?
Does it happen suddenly or just gradually worsens until it is total snow?
Or, do you get the 'blue screen' if it has this function rather than snow?
Does the tuner still work?
Conversely, does PLAY work but not the tuner?
Do other functions like FF and REW always work?
How is the time it sits turned off related to how much on time you get?
Have you verified that the TV is fine?
Is it possible that the VCR is covered up/closed in/installed with inadequate
ventilation?
It could be a loose connection or bad component. The usual way to narrow
down the possibilities is to use what is called 'cold spray' or 'circuit
chiller' on the appropriate sections of the circuit board until you locate
the component that is failing with when it gets hot. I once had a VCR that
needed a little fan blowing on it to keep it happy - much easier solution
than actually hunting down the fault.
If play or record just stopped and the tape unloaded, it could also
be a mechanical problem like a marginal idler tire, idler clutch, or
worn belt.
First confirm that the correct fuse type and value was used for this
particular model and revision number.
Of course, measurements of the supply current on the bench show a wide
safety margin (i.e., 2:1).
I don't suppose there was any mention of what was being done when it
stopped working?
While monitoring the current, try really exercising the FF and REW,
switching between editing/tape movement modes, performing FF and REW
to the end of tape stops, etc. These are where I would expect to see
current spikes. It may be some peculiar combination of actions that
results in a momentary jam or conflict.
Unless of course it is just some cosmic connection that takes place every
3 months!
Overall, VCRs are quite tough. However, falling in just the wrong way
can do substantial and possibly not immediately visible damage.
If you take it in for service, the estimate you get may make the national
debt look like pocket change in comparison. Attempting to repair a VCR
that has been dropped is a very uncertain challenge - and since time is
money for a professional, spending an unknown amount of time on a single
repair is very risky. There is no harm is getting an estimate (though
many shops charge for just agreeing that what you are holding is a VCR!)
This doesn't mean you should not tackle it yourself. There may be
nothing wrong or very minor problems that can easily be remedied.
First, unplug the VCR even if it looks fine. Until you do a thorough
internal inspection, there is no telling what may have been knocked
out of whack or broken. Electrical parts may be shorting due to a broken
circuit board or one that has just popped free. Don't be tempted
to power the VCR even if there are no obvious signs of damage - turning
it on may blow something due to a shorting circuit board.
Then, inspect the exterior for cracking, chipping, or dents. In addition
to identifying cosmetic problems, this will help to locate possible areas to
check for internal damage once the covers are removed.
Next, remove the top and bottom covers and front panel. Check for
mechanical problems like a bent or deformed cassette basket, broken or
cracked plastic parts, and anything that may have shifted position or
jumped from its mountings.
Carefully straighten any bent metal parts. Replace parts that were
knocked loose, glue and possibly reinforce cracked or broken plastic.
Plastics, in particular, are troublesome because most glues - even plastic
cement - do not work very well. Using a splint (medical term) or sistering
(construction term) to reinforce a broken plastic part is often a good
idea. Use multiple layers of Duco Cement or clear windshield sealer
and screws (sheetmetal or machine screws may be best depending on the
thickness and type of plastic). Wood glue and Epoxy do not work well
on plastic. Some brands of superglue, PVC pipe cement, or plastic hobby
cement may work depending on the type of plastic.
Cycle the cassette loading and tape loading mechanism manually by turning the
appropriate motor shaft, if possible. Check for free movement of the
various parts of the tape transport.
Inspect for any broken electronic components - these will need to be replaced.
If the fluorescent panel is broken, you can run the VCR without it but
of course will not be able to see any front panel displays. Check for
blown fuses - the initial impact may have shorted something which then blew
a fuse.
There is always a slight risk that the initial impact has already fried
electronic parts as a result of a momentary short or from broken circuit
traces and there will still be problems even after repairing the visible
damage and/or replacing the broken components.
Examine the circuit boards for any visible breaks or cracks. These will
be especially likely at the corners where the stress may have been greatest.
If you find **any** cracks, no matter how small in the circuit board, you
will need to carefully inspect to determine if any circuit traces run
across these cracks. If they do, then there are certainly breaks in
the circuitry which will need to be repaired. Circuit boards in VCRs
are never more than two layers so repair is possible but if any substantial
number of traces are broken, it will take a great deal of painstaking
work to jumper across these traces with fine wire - you cannot just run
over them with solder as this will not last. Use a fine tipped low wattage
soldering iron under a magnifying lens and run #28-30 gauge insulated wires
between convenient endpoints - these don't need to be directly on either
side of the break. Double check each connection after soldering for correct
wiring and that there are no shorts before proceeding to the next.
If the circuit board is beyond hope or you do not feel you would be able
to repair it in finite time, replacements may be available but their cost
is likely to be more than the VCR is worth. Locating a junk VCR of the
same model to cannibalize for parts may be a more realistic option.
Once all visible damage has been repaired and broken parts have been replaced,
power the VCR up and see what happens. Be prepared to pull the plug if there
are serious problems (billowing smoke would qualify). Determine if it
appears to initialize correctly - without shutting down. Play a garbage
tape to determine if there are any problems that might damage the tape.
Watch and listen carefully for any evidence of poor tracking, video noise,
tape speed instability, or weak or muddy audio that might indicate that
tape path alignment requires further attention. Listen as well for any
unexpected mechanical sounds that were not there before.
Very likely, the VCR will be fine, you can replace the covers, and now find
a more secure spot for it to prevent this sort of event in the future. Use
your own judgment with respect to the cat.
Unless this is a really sophisticated (i.e., costly) unit, I doubt whether it
will pay you to take it anywhere for repair. Even if it is successfully
repaired, its reliability may be questionable. Furthermore, as with equipment
that has been dropped or physically abused, few repair shops will be inclined
to touch the job. They really don't like challenges of this sort.
That leaves you!
If anything got wet with saltwater and it has been just sitting, you can
probably forget it. Without immediate attention (and I mean immediate, not
later, not tomorrow, NOW!), saltwater corrosion can set in very quickly and
attacks electronic components, circuit board traces, cable wiring, and
mechanical parts. The only thing worse might be a peanut-butter-and-jelly
sandwich 'played' in your VCR. On second thought, that probably would not
be all that bad.
Although it is probably too late, the first thing to do when electronic
equipment gets wet is to remove the power source - pull the plug or
remove the batteries. Don't be tempted to apply power until you have
determined that everything is completely dried out inside and out.
DO NOT use strong solvents anywhere! These may attack various plastic
parts or cause internal damage to electronic components.
The following was written assuming sand, salt, and liquid contamination
everywhere! Modify based on your specific situation.
Mechanical intensive care:
Lubricate all bearing points with a drop of light machine oil - electric
motor oil, sewing machine oil, etc. (Never never never WD40). Lubricate
gears, cams, and sliding parts with a light plastic safe grease such as
Molylube.
Parts like the idler clutch may need to be disassembled to get at
the friction felt. Other mechanical parts like cam gears may need
to be removed to be properly cleaned. Don't mess up the timing
relationships when you do this!
Electronic intensive care:
Note: drying time may be quite long. For parts with inaccessible areas
like membrane keypads, you may need to wait a week before normal operation
is restored. Be patient!
Once everything is completely dry as a bone and reassembled, power it up but
be prepared to pull the plug or pop the batteries if there are serious problems
See if the display comes alive and the transport appears to initialize.
Attempt to play a garbage tape to determine if there are any mechanical
problems that might damage the tape. Look and listen for any abnormalities
which may require additional attention. Then address specific problem areas.
Also see the section: VCR was dropped for additional
info.
Obviously, this description is very simplistic. The important thing is
to get every last grain of sand, salt, and other contaminants off of the
mechanisms and circuit boards quickly.
As noted above, moisture may collect inside certain electronic parts and
it is essential that these be dried completely before attempting to apply
power to the unit. If you do not, at best it will not work properly and
you may do additional serious damage due to short circuits.
For the mechanics, the same applies though this is trickier since certain
parts need to be lubricated and these may not be readily accessible or
obvious. Don't be tempted to overdo the lubrication - too much is worse
than too little.
For camcorders, some parts of the optics or enclosed DC-DC converters
may be impossible to access and clean of scum.
If it is only slightly crinkled, the tape may be salvageable (though it will
never likely play without some dropouts). How serious is 'serious'? Hard to
say but ironing may help. See the section: Uncrinkling a
crinkled tape.
However, if it is broken - even partially, or stretched and scrunched, I
recommend you throw it away (and make sure no one else can pull it out of
the trash and ruin *their* VCR!).. An imperfect splice or seriously crinkled
section of tape can shatter your video heads - the most expensive single part
in a VCR. If it is something you really treasure, than what I would do is
to follow the procedure below.
Note: If you have never seen the inside of a video cassette, try the following
on a couple you really don't care about first so that if you screw up, there
is no great loss. Too bad AOL doesn't send out Internet software on video
cassettes, huh?
CAUTION: The video tape itself is really really thin and easily crinkled.
Be very gentle when handling it and avoid touching the oxide (dull side)
if at all possible.
Cassette 1 has the first section of tape (before the break) and uses
one empty reel from the garbage cassette for the supply reel. Rewind
this to the beginning.
Cassette 2 has the second section of tape (after the break) and uses
the other empty reel from the garbage cassette for the takeup reel.
Use the little plastic plugs that came from the garbage tape reels or
some adhesive tape to connect the tape to the reels.
Filip (I'll buy a vowel) Gieszczykiewicz (filipg@repairfaq.org) is a
little more definitive about this: "I find the destruction of it more
fulfilling :-) ... put it in a paper bag and smash the life out of it
with a big, heavy hammer - or a small ball hammer for an even higher
satistfaction ratio :-) "
The idea is to never have a splice in a VHS cassette. (Even a seriously
crinkled tape such as might result from a tape eating incident can damage
the heads.) It is possible to splice safely but as noted, it can be quite
costly if you don't get it quite right.
Just winding the damaged section back into the cassette and then FFing or
REWing as appropriate to put several layers of tape on top of it may help.
Leave it like that for a few days and then carefully return to the crinkled
section to see how it is doing. WARNING: Do all this on a VCR that DOESN'T
have an instant response transport so that there is no chance of the video
heads contacting the damaged part of the tape. You may have to do this a few
times.
Passing the damaged section (backing side) around a blunt edge (like a table
top) back and forth a few times may help as well.
(From: Paul K. Sagi (paul_sagi@astro.com.my).)
I had a go at a seriously crinkled VHS tape that my mom was wanting to show
her class at temple. I put the crinkled section between pieces of the kind
of paper that is sold for some kind of cooking use, can't remember what it
is called. I then ironed it (heat only, no steam) and it worked OK except a
couple of seconds dropout."
(From: Steven Van Assche (steven.vanassche@yucom.be).)
CAUTION: Use with care!!
I use the following: Get your iron, the one used for T-shirts, not your
soldering iron! ;-)
What I do:
Now, to play it safe, copy it to another tape. and mark the old one as damaged.
The most important factor here is heat: Too hot and you will burn the tape
instantly while too cold and nothing will happen. It is best to start from
cold to warm, and slowly increase the heat until you see an improvement...
At this point, you should see something that looks like VHS Cassette - Inside Top View.
When you reassemble the cassette, take care to avoid crunching the tape under
the hinged door - depress the unlock button on the side and lift it clear if
needed.
Note that some designs are very hard on cassettes - yanking at the tape since
only increased tension is used to detect when the tape is at the end. These
may eventually stretch the tape or rip it from the reel. As noted, I don't
really care much for the use of tape rewinders as normal use of rewind and
fast forward is not a major cause of VCR problems. Sluggish or aborted
REW and FF may simply indicate an impending failure of the idler tire or
idler clutch which should be addressed before the VCR gets really hungry
and eats your most valuable and irreplaceable tape.
Problems with tape rewinders are usually related to a broken or stretched
belt or other broken parts. These units are built about as cheaply as
possible so failures should not be at all surprising. The drive motor can
suffer from any of the afflictions of similar inexpensive permanent magnet
motors found in consumer electronic equipment. See the section:
Types of Motors in VCRs. A broken belt is very
common since increased belt (and tape) tension is used to switch the unit
off (hopefully). Parts can pop offof their mountings. Flimsy plastic
parts can break.
Opening the case is usually the biggest challenge - screws or snaps may
be used. Test the motor and its power supply, inspect for broken or
dislocated parts, test the power switch, check and replace the belt if
needed. That is about it.
(From: Jeroen H. Stessen (Jeroen.Stessen@philips.com).)
JVC owns the patent for VHS. JVC has made a deal with Macrovision that from
a certain date in the past *no* VHS recorder licensed by JVC shall be able to
record any video signal that contains Macrovision's copy protection pulses.
Any video recorder from before that date (VHS or other) might well work OK on
the altered video signal! The copy protection pulses upset the video AGC and
H-sync. TV's usually don't have a video-AGC.
Thus the whole idea of the Macrovision method is to disturb the video AGC
that is inside every VCR - the manufacturers even *must* make the video AGC
sensitive to those pulses!
In the TV, the horizontal sync processing may be disturbed by the Macrovision
pulses. Indirectly that also disturbs the DC clamping circuit. So you may see
horizontal phase as well as brightness disturbances at the top of the picture.
The stabilizer box removes the extra pulses and makes it into a normal video
signal again. No VCR should ever know the difference, so they should all record
properly again.
At the same time, all TV's are required to ignore the copy protection pulses.
As a TV-designer I can tell you that this is sometimes far from trivial. Not
in the least because in the beginning we were not included in "the deal".
There may be TV's around whose brightness and/or sync will be disturbed by
the Macrovision pulses. Officially, this is the reason for existence of the
stabilizer boxes: to view better, not to copy better. Unofficially, they are
sold for copying, of course.
Keep in mind that the Macrovision 'standard' (pardon me) has been improved
several times. Old decoders may not be able to cope with newer tapes. In order
for the decoder to key out the pulses in the vertical blanking interval, it
must first synchronize properly itself. That process too may be disturbed (by
extra pulses on newer tapes to older decoders).
Those Macrovision a**holes are smarter than you think. Unfortunately, their
signal may also disturb some TVs which are used legitimately. And then it
becomes *our* problem too.
The next step will be that digital-TV decoders will output an analog TV
signal with Macrovision copy-protection pulses so that you may watch but
not record your pay-per-view program. Same problem, same solution ...
And I thought that PAL/SECAM/NTSC were *standards*, sigh ...
Look at it this way. The reason that you see changes in brightness is
that the "protection" signal that is added makes the unit's AGC (auto-
matic gain control) think that the level has shifted, when it hasn't.
So it adjusts to compensate.
So if you have an older VCR without AGC (or a mild application), it may
not be affected as much (or at all, after passing through a "stabilizer"
box). If the sensitivity of the AGC is high (like it is on most JVC's)
and the response-time is short, any small amount that leaks through
will still cause problems.
For those familiar with the electronic circuitry in VCRs, both the time
constant in the RC circuit for response-speed, as well as the AGC sensitivity
can be adjusted by manipulating simple resistor values. I don't have any
specifics on this (and it varies on different machines), so don't bother
asking for it :-).
But at least you now know why some decks react differently.
Of course, as with so many other problems, poor quality or well worn tapes can
result in erratic closed caption decoding. Therefore, I would not recommend
diving into the bowels of your VCR before trying out some other tapes.
(From: Thomas D. Kite (tom@olive.ece.utexas.edu).)
Sounds to me like the head switching point is too far down the screen, i.e.
the point at which the VCR switches between the video signals from the two
heads is too late. You can check this if you have a TV with vertical hold.
Set the hold to give a stationary or slowly rolling picture so that you can
see the head switch, which will appear as a tearing of the picture. This
should occur during the blanking period, but I suspect that your VCR is
switching sometime later. If so, open it up and look for a preset on the
main board labeled 'Head SW PT' or something like that. Twiddle it so that
the tearing backs up the screen into the blanking part (again, do this while
the picture is rolling slowly). Hopefully, this will mean your VCR has done
its switching by the time it gets to Line 21, and the CC information will be
intact.
(From: Richard Beeler (vcrmonthly@earthlink.net).)
This could be Copy Guard on tapes interfering with the closed caption decoding.
We had one that was doing the same thing on some pre-recorded tapes and not
others. We finally had to add a 'video stabilizer' between VCR and TV - that
corrected the problem.
I recently repaired a Panasonic VCR with a dangling F-connector. It required
removing the cover, main board, unsoldering the A/V block and part of the
power supply, just to get at the RF modulator. Then it was a simple matter
of resoldering the center conductor to the printed circuit board (fortunately,
nothing else was damaged) and the shell of the F-connector to the metal box.
From: Glenn Watkins
We get a lot of sets with broken "F" connectors broken off - both VCR's and
TV's. The job can be quite involved depending on the exact set. It may take
an hour just to open it, remove the tuner or RF modulator and open the case.
Then if you're lucky, there is no additional damage inside the unit due to
people probing with pencils, screwdrivers, etc.
On some TV's including Sharp, there is a antenna(cable) isolation device
that connects between the tuner and antenna. This device comes in a few
flavors and is very easy to install if broken. I've seen them as cheap as
$4.95 each mail order.
Your VCR probably was made by Hitachi (Sears is one of several brands that may
be manufactured by Hitachi). If so, probably your DC to DC converter went bad.
Please note that the the converter is close to the front of the VCR and not on
or near the main power supply board.
Also check the IC protector (possibly ICPN5) as it may have blown. You should
also replace the two 47 uF 50 V and the 100 uF 35 V capacitors near the DC to
DC converter. These are known to go bad resulting in failure of the DC to DC
converter.
Complete repair kits are available from suppliers like MCM Electronics. These
will include all components likely to have gone bad.
For some models:
(From: Sire Johnathan (sirejohn@bbs-la.com).)
Behind the Channel selector is an upright PCB. on the upper inside corner
find a 1/2" sq. transformer can with top hole and slotted core adjust.
The schematic nomenclature is T101 or T102. Next to it, find a TO-220 power
transistor. Replace the Pwr Xstr, filter caps in secondary side rectifier
with DOUBLE the voltage ratings, and a small choke (L1?) that feeds primary
power to the power transistor (fuses open). When working properly, current
draw through primary circuit should be less than 200 mA.
JVC, huh? How did it die? What are the symptoms? Major tracking problems?
Eats tapes? JVC VCRs of that era tend to shed parts in the tape loading
mechanism - easily fixed. Unless it is a serious electronic problem (there
is a minor one which results in similar symptoms - see below), a service
manual may not help. And even then, it may not have the information you need.
Check the roller guide assemblies (see the sections: "Parts of the tape
transport in a VCR" and "General tape path alignment problems").
There are two types of failures that occur frequently on various JVC models:
Alternatively, replacement roller guide assemblies are available.
WARNING: do not attempt to load a tape if a roller guide assembly can be
lifted off of the track - it may smash the rotating video heads - very
expensive lesson. Of course, it may already be too late :-(.
To get at the bottom of the roller guides or hinges, you will probably have
to convince the VCR to start loading a tape and then pull the plug just as
the mechanism is in a position where you can get to it.
In some severe (or shall we say, strange) cases, good and bad/no video may
occur randomly each time the VCR enters PLAY mode but will remain that way
until the tape is unloaded.
(From: Mark Shoberg (mewzaq@webtv.net).)
When replacing the 3.3uf cap on the motor board (this is for the older
bottom mounted types) just cut away the plastic piece covering it a little
bit. This way you don't risk damaging the video heads and it is easier as
well.
(From: John Poulton (John@TellyCare.freeserve.co.uk).)
This is a very common problem on these machines. To check it out carry out
the following check:- Set the machine to play a pre-recorded tape. While
observing the picture on screen, stop the head drum rotation by pressing
your fingers on the top surface of the drum for a fraction of a second. The
instant the drum stops, release it and let it start up again.
This must be done very quickly, otherwise the machine will shut off. If you
find that each time this is done the picture re-appears in a different
state, it means that the 3.3uF capacitor on the board of the head motor is
faulty. It can be replaced without removing the deck from the cabinet if a
small section of the plastic base is cut out.
There were more Magnavox models made by JVC in the early 90's than many
people realize. The following models were all made by JVC:
VR1835, VR3440, VR9020, VR9040, VR9140, VR9142, VR9160, VR9162, VR9240,
VR9241, VR9260, and VR9362.
All used the same chassis which JVC used in their HR-Dxxx series of VCRs.
See the section: JVC tracking problems and dropped
parts.
(From: John (johnbrewer@webtribe.net).)
Most of these faults are caused by either the mode switch or that
horrible plastic thing on the end of the loading motor shaft.
A number of Panasonic and other Matsushita brand clones use a
switching power supply which has a couple of common failure modes.
The same power supply is used with minor variations in a wide variety of
Panasonic (and clone) VCRs from the 1980s and 1990s (and may continue to
this day). Depending on the specific model, there may slightly different
output voltages and number of outputs but the general organization is
identical. These use discrete components throughout with feedback from
the primary output (5 to 5.2 V depending on model) using an optoisolator
to essentially short out the drive to the main chopper transistor (Q1) when
the output equals the desired voltage. The most common problems found
with any of these supplies is dried up electrolytic capacitors. Generally,
the first to go will be C16 and C17 on the +5.1 VDC line and/or C21 in the
feedback path (actual part type and number may vary slightly with model).
Symptoms will be either that the primary output is somewhat low (4 to 4.5 VDC)
or that the supply has gone overvoltage and blown the protection zener (D15)
resulting in a high pitched whine as the chopper struggles to drive current
into a short circuit (this usually doesn't damage any other parts if caught in
a reasonably timely manner). If any capacitor related problems are found,
it is a good idea to replace all the electrolytics in the supply. Model
specific capacitor kits as well as total rebuild kits are available from
places like Studio Sound
Service and MCM Electronics.
Some of the sources listed in the section: Suggested
Parts Suppliers sell power supply rebuild and capacitor kits. Unless
your power supply is missing, one of these kits will probably fix it - and
all you need to know is how to solder!
Also see the section: Quick tips for troubleshooting
Matsushita/Panasonic SMPSs.
(From: Ken Koskie (aw345@lafn.org).)
This may be one of the RCA VCRs plagued with intermittent diodes. RCA
recommends replacing the following diodes; D108, D109, D110, D112, D114,
D1103 and D1104. Their part number for the diode kit is 201066.
(From: Frank Fendley (frank.fendley@datacom.iglou.com).)
Common solution for this - replace D108, D109, and D110 - even if they test
good with a meter. ECG125 works well for this (2.5A/1000PIV). While you
are at it, also replace D105, D106, D111, D112, D113, D114, using the same
replacement. Samsung must have purchased 40 billion bad diodes when they
built these units. Funny thing is, they almost always test OK with a meter
but replacing them fixes the problem. Apparently they go open under operating
voltage, but not under the lower voltage provided by a meter.
Alternate solution (fairly uncommon) - replace IC201.
(From: Mark Z. (zmachar780@aol.com).)
If this model is the type I think it is, there is an open diode along the
inside edge (toward the mechanism rear) of the top circuit board. There is
actually about 7 diodes which tend to go bad in these due to underrating.
Five are in the area I mentioned, that is two along the edge at the middle
of the board, and three further back, and two are located under the power
transformer. Other problems, such as no display or no power, will occur if
any of the others go bad. Suggest you replace them all; Any decent 1N4007
or such will do fine. Radio Shack has "2.5A 1kV" diodes which would be fine.
For some RCA VCRs with somewhat similar symptoms:
(From: TVman (tvman@newwave.net).)
For the RCA VR321 which appears dead, clock display may come on after a few
minutes, Q1 runs hot: Replace: C09 (22 uF, 16 V) non polarized capacitor in
power supply.
(From: Chuck Yung (cbelect@pce.net).)
For the Samsung VR3711, there are a total of seven diodes that should be
changed, they are: On the main board: D108, D109, D110, D112, D114; In the
power supply: D1103, D1104.
Many Samsung VCRs, (and possibly other makes) use a DC to DC switching
power supply built onto it's own separate, shielded PCB which plugs
into the main circuit panel, and is secured in place by two or three
screws. On this power supply, located right next to the switching
regulator transistor (Q1) there is a 16 V, 22 uF, non-polarized
electrolitic capacitor which frequently fails, probably due to
constant exposure to the heat generated by Q1. (Refer to Sansung VCR
Power Supply Parts Location.) When this capacitor is faulty, the
VCR's flourescent display will usually flash about once per second
when the set is first plugged in, and possibly after some time, the
display will become steady and the unit will function normally. In
extreme cases where the capacitor is completely open the display may
never light up at all. If the power supply is removed from the VCR,
and tested under a no-load condition, all voltages will likely appear
normal, giving the false impression that the VCR is overloading
it. When working on this panel, please bear in mind that it is
directly connected to the 120 VAC power line, and therefore presents a
significent danger of electrical shock - BE CAREFUL.
The chassis of Sharp VCRs come in several flavors. Here is a description of
two of them with respect to getting at the mode switch:
To access the mode switch, unplug the connectors, remove the single belt
that drives the eject mechanism, and remove the 3 screws. It should now be
possible to detach the entire assembly. Underneath, you will see a disk
with a keyed center hole - this is what must be replaced with the same
orientation as it was before removal. The disk snaps off easily revealing
the tracks and contacts of the mode switch. Thoroughly clean and slightly
increase the spring pressure of the contacts. Replace in reverse order.
Make sure the post slips into the keyed hole as you replace the assembly
and double check that it is seated before tightening the screws.
Timing marks: There is at least one critical timing relationship that needs
to be preserved when the loading gear assembly is removed. I recommend that
you put your own timing marks on all gears before loosening the 3 screws
that anchor this unit. You will need to unsolder 4 connections as well
before it will come free. Once the bottom of this unit is accessible, the
mode switch can be snapped apart and cleaned.
I believe this is best done with the VCR in the unloaded and ejected state.
However, there are still a couple of levers that will need to engage properly
when the loading gear assembly is replaced. These press on internal cams
that are hidden when everything is together. Much fun.
(From: Lill Tommy (tommy@caves.net).)
For newer models like the Sharp VC-H956, it may act like a mode switch problem
but it isn't and you need to change the takeup and supply reel LEDs and cam
switches and D706 to D709. (Sharp part # for D706 and 707 - RH-PX0252GEZZ;
for D708 and D709 - RH-PX0253GEZZ).
If you forgot to count the turns or the nut had originally loosened up, just
center its height within the range over which the tape moved stably past the
first fixed guidepost and/or A/C head. Then confirm reliable loading and
unloading with several different tapes. Try using forward and reverse search
to assure that the tape isn't moving up or down on the guides. Make sure
there is absolutely NO tape edge damage.
Someone gave me a fancy Sony HiFi VCR with the request "I will pay up to $150
to fix it. Circuit City said that it could not be repaired for less than $250
because my kids had gotten into it and recommended replacement" (I wonder why).
It was the stupid loading arm. Obviously, the grade-A techs at Circuit City
were either under orders not to suggest repairs if they could get away with it
and/or had never even taken the top off of the thing because the owner had
mumbled something about his kids.
I could have made a bundle off of that. I could have had a nice VCR for
nothing. I just gave it back and told him about the bit of cleaning and
drop of oil.
(From: Sire Johnathan (sirejohn@bbs-la.com).)
I recall well from counting turns until that elastic nut lifts off the stud is
very repeatably 6.5 - 6.75 turns. Checking it with the Sony height specs is
always within limits. Don't forget to check the smooth running of tape over
this 1/2 load pre-threading guide pin in the reverse scan direction. The tape
should maintain same height when changing rapidly between FWD SCAN and REV
SCAN. A worn conical pinch roller can cause tape height shifting and tape
edge-rippling or top-slacking because the pinch roller becomes the primary
tape guide in REV SCAN. Changing quickly between REV SCAN & PLAY modes while
monitoring normal linear audio treble and tracking can reveal any mis-skewing
of the tape path as it 'returns into the groove' in PLAY mode. Sony pinch
rollers are notoriously short-lived causing most tape edge-rippling and
mistracking. BEWARE of 3rd party substitute parts as they are frequently out
of tolerance and poor bearings necessary for Sony mechanisms.
Later Sony VCR's have "emergency" codes that show up in the Fluorescent
Display on certain failures. The code shows up in the "seconds" position
and they are as follows:
Play a tape until the VCR shuts off and then check the failure code to help
diagnose the problem. These codes are cleared when AC is removed or when
another function button is pushed.
Some Sony VCRs may use the error coding summarized below:
Others may use an "hours-minutes" format:
(From: John Poulton (John@TellyCare.freeserve.co.uk).)
The centre part tells which mode the machine was in when the fault occured
(the "minutes" part). It is the last part of the code that is important
(the "seconds" part).
The code is as follows
My local repair shop diagnosed the problem for $30 and gave me a $200
estimate to fix it. 3 questions:
To satisfy the curious: the symptoms were a jittery picture on playback of
tapes. The problem began with playback in EP mode only (the picture would
freeze and hi-fi audio would "ratchet" as though the tape had come to a halt).
It progressed until this started happening in SP mode as well. The problem
got much worse the longer the unit was running (or the farther into a given
tape I watched...)."
(From: Bob Groger (BobG1@msn.com).)
This is a common problem, but you don't need to replace the motor! Sony sell
a new bearing assembly for about $25. There is a service bulletin out on this.
The bearing housing bends after a period of time from pinch roller pressure.
The new one is much stronger. Quick but temporary cure is to grasp the top of
the bearing housing with big pliers and bend slightly towards pinch roller.
This is NOT a guarantee!
(From: ZMachar780 (zmachar780@aol.com).)
They have a lot of bad capstan motors on these. The bearing collapses a little,
then the flywheel scrapes on the drive coil. Sony sells a replacement bearing
assembly which would save a few bucks over a cap motor, but frequently the
capstan shaft is worn anyway and should be replaced. Sony will ID the part
number(s) and sell you the part directly (on a credit card). Call them at
800-282-2848.
(From: Willis Chung (nikonkidf3@aol.com).)
This is the classic Sony capstan motor bearing problem. The capstan motor is
a direct drive unit with a large flywheel/magnet assembly mounted just below a
set of flat coils. The bearing that the capstan turns through is also part of
the bracket that supports the motor. With time, the bearing wears out,
allowing the capstan to tilt ever so slightly. This tilt causes the capstan
flywheel to come into contact with the coils, causing a scraping sound,
intermittent pauses, and eventually causing the motor electronics to die.
Stop using the VCR now to prevent damage to the motor's electronics. The
capstan motor bearing can be replaced without having to replace the entire
motor. The bearing is available direct from Sony for about $12, but the
entire motor costs about $45 to $55.
For the SLV-575, the part number for the bearing assembly is X-2625-269-1.
However, replacements for other VCRs have different part numbers - best to
check before ordering.
Replacing the bearing is straightforward, and anyone can do it (well just
about anyone!).
The repair is easier to do than to explain!
(From: David A. Sanders, II (capeone@aol.com).)
The bearing part number for the Sony SLV-R5UC VCR is X-2625-356-2. The motor
part number is 8-835-350--02. Check the winding on your motor. Many times
when the bearing fails, it allows the magnet assembly to rise, which in turns
starts to cut into the windings.
Belts and idler tires are always the first thing to check for this sort of
problem but older Symphonic/Funai VCRs (Those without the 'quickstart' type
mechanism) also have a small rubber bumper/stop for the brake levers, etc.
on top of the deck by the tape reels. It wears out and then the lever
catches don't engage properly. The old mechanism was replaced by a compact
direct drive type which is mounted directly on the PCB in 1993 (at least on
the European PAL models).
Part #8059-02-23 is available at electronics distributors such as Fox
International in Ohio or MAT Electronics in PA. Symphonic/Funai Corp,
100 North St, Teterboro, NJ 07608 phone 201 288-2606. Alternatively,
just wedge a bit of plastic inside the rubber bumper to fatten it a bit
or just turn it around to expose the unworn side. This works just as
well as a replacement part.
On the subject of the funai type rubber bumper problem I would like to give an
additional symptom of that problem. After repairing hundreds of these units one
goofy symptom I've found is the fact that customers may complain that the
machine will eject a tape that is fully rewound and will play a tape if it is
anywhere else on the tape. The FF/REW problem may or may not show up at this
time. Also note that the best cure is the original part from symphonic. I
have found that generic bumpers from MAT or MCM for example have cost me
callbacks because there just not cut perfectly.
(From: Matthew L. Kruckeberg (MKRUCKEBERG@pol.org).)
I have run into a few of these Funai mechanisms where the replacement
rubber bumper is too thick causing the mechanism to lock up in various
positions. If you still have the original one try reinstalling it
backward and see if your problem goes away. I would not recommend
turning the bumper around permanently since the repair is short lived due
to deterioration of the rubber but it will generally work at least for
test purposes.
This is a common problem with certain Zenith VCRs. It is caused by the copy
guard present on certain rental tapes. Zenith will modify these VCRs at no
cost. The modification inverts the sync pulse by adding a transistor, a
resistor and modifying the circuit board. If the model number starts with VRJ
or VRL (possibly others as well), this is likely to apply.
If you don't want to do the modification yourself but really want to sound like
you know something, suggest that the problem is covered by Zenith Field Service
Bulletin #94-16 :-).
Two very similar modifications follow:
(From: Guitarzan (guitarzan@aol.com).)
Locate IC201 on left of top circuit board and IC 202 on right. Cut the trace
between IC201 pin 56 and IC202 pin 17. I've found it easier to remove the wire
jumper directly beside pin 56 as this leaves a place to mount the transistor.
Install a general purpose NPN transistor (ECG123A, Zenith 921-2161 or 921-2134,
or 2N2222) with base to IC201 pin 56, emitter to ground, collector to 10K 1/4 W
resistor, other end of resistor to W2H5, or another +5 V source. The current
drain is very minimal so pick the most convenient source of +5 V.
All this does is invert the servo pulse and keeps the circuit from becoming
'confused'. If only it would do the same for me.
Fire it up and all should be well. Try an EP tape, if its installed
incorrectly, EP won't track at all.
(From: Brian Hughes (bkhughes@usa.net).)
Required parts: Small signal NPN transistor (ECG85, ECG2357, KRC103M), 10K 1/4
W resistor.
Locate IC 201 on the main circuit board, cut the trace between W2C4 and IC201
Pin 56. Solder resistor between W2C4 and W2H5. Solder transistor as follows:
Base - IC201 Pin 56, Collector - W2C4, Emitter - IC201 Pin 5.
Insulate all exposed leads ( I like hot-melt glue, it secures things in place
as well.) Finis.
Why it works: Many pre-recorded tapes have timing marks inserted in the
control-track signal. These extra pulses confuse the servo circuit in these
machines. This modification inverts the signal before it reaches the servo so
that it is not detected.
The actual video heads are the nearly microscopic transducers that contact
the tape and magnetically record or playback the video information. The
upper cylinder is the entire rotating assembly including the video heads.
The heads are aligned and locked in place on the upper cylinder at the time
of manufacture and this alignment should never be touched.
(Note that the terms 'video heads' and 'upper cylinder' are often used
interchangeably but strictly speaking this is not correct.)
The heads themselves are made from ferrite which is an extremely hard
ceramic magnetic material which is also very fragile. The head chips
can be seen at the very bottom of the rotating upper cylinder. The actual
construction is of a 'C' shape with a very small gap between the arms of
the 'C' - about 1 um or so. This is filled with with a non-magnetic
material to force the magnetic field out of the head into the tape and
to prevent material from collecting in the gap. A few turns
of fine wire form the coil of an electromagnet for recording and as a pickup
coil for playback. If you look at a head chip from below (on a cylinder that
has been removed) you can see the coil and the shape of the core, though
you will not be able to tell if a head is bad or worn by this inspection
unless there is obvious damage). A powerful microscope is needed to even
see the gap.
VCRs are described as having '2 heads' or '4 heads' or whatever. This
actually refers to the number of head gaps and not actual head chips though
usually this is the same number. However, two head chips may be placed
very close together and thus appear to be a single head when in fact there
are a pair of head gaps. Therefore, without a close examination, there may
only appear to be 2 heads when in fact there are 4 - in 2 pairs. You are
not being short changed.
Two heads are required for any play, record, or search function. Usually,
these are exactly 180 degrees apart - directly opposing one another on the
upper cylinder. With 4 head (or 3 head or 5 head) VCRs, various combinations
of heads are used for each mode to optimize record or playback video quality
by selecting a pair of heads with optimal widths and other characteristics.
These may end up not being exactly 180 degrees opposed requiring video delay
line to line up the two video fields in a video frame properly. This
complicates head testing as it is not always obvious even which set of
heads is used in any given mode.
An additional pair of opposing heads is required for HiFi VHS audio and
another one is present if the VCR has flying erase head. Usually, there
is only a single flying erase head - it is double width and clears a pair
of tracks (fields) on each pass. So, there may be up to 7 (or even more)
heads competing for space on the upper cylinder!
Also, see the section: Video head construction.
(From: Andy Cuffe (baltimora@psu.edu).)
It's impossible to use more than 2 heads for normal playback. If you
look at the theory of VCR operation you will see why this is so. VHS
camcorders do use 4 heads for normal play, but thy do that to reduce the
size of the head drum. On an NTSC 4 head VCR 2 heads are used for SP
(2hr) and the other 2 are used for LP (4hr) and EP (6hr). All 4 heads
are used for still, slow and search (it picks the head with the highest
RF output). On my Sony SL-HF1000 you can actually see a difference in
the pattern of switching points in search depending on the tape.
On a PAL machine 2 heads are used for SP (3hr) and 2 heads are used for
LP (6hr). All 4 heads are used for still, slow and search just like in
NTSC. The only difference is the that the head gaps are designed for
PAL tape speeds. A good 2 head should look almost identical to a good 4
head.
CAUTION: Do not touch these mounting screws or the height adjustment screw
accessible from above the drum. It is virtually impossible for these to
become loose or misadjusted on their own and alignment in the field is not
possible except by trial and error.
These structures may be viewed under a strong (e.g., 10X) magnifier though
the actual record/play gap between the pole pieces will not be visible except
under a powerful microscope. It is filled with a hard non-magnetic material
in any case.
The thickness of the ferrite chip is about .1 to .15 mm but the width of the
active part of the pole tips narrows down to around .03 mm. This is one of
the dimensions that is optimized for various special effects in VCRs with more
than 2 video heads.
The gap azimuth angle of + or - 6 degrees (for VHS) is implemented by actually
twisting the pole pieces during the molding process. This is actually visible
if you look carefully with the magnifier even though you cannot actually see
the gap. (The azimuth angle has obviously been exaggerated in the diagrams
below due to the limitations of ASCII art.)
The coil used to generate the magnetic field during recording and to sense the
magnetic field for playback consists of a dozen or so turns of fine insulated
wire with a typical resistance of 1 to 1.5 ohms.
HiFi audio head construction is generally similar except that the gap azimuth
angles are +/- 15 degrees instead of +/- 6 degrees.
Damage to the core, pole pieces, or coil, and oxide on the surface or clogging
inside of the core can be seen with the magnifier in many cases.
This is a view as would be seen from the bottom of the upper cylinder:
Note that the two video heads in each pair are close together and have
opposite azimuth angles. This permits them to both be active during
special effects modes - whichever one has the stronger video signal is
used. Being close together, you might mistake them for a single video
head and think you were short-changed and only got a 4 head machine!
The actual head gaps are way too small to be seen in even the closeups but
the pairs of coils on each ferrite core are clearly visible.
For camcorders where compactness is important, the drum diameter is reduced
to 2/3rds of this or 1.65". However, in order to record and playback
properly, 4 heads equally spaced around the circumferance of the drum with
alternating azimuth angles are required in all modes. The drum speed is also
increased to 3/2 of the normal 1800 rpm or 2700 rpm. If you work this out,
you will find that this results in exactly the same writing speed and track
length when successive heads for each video field are located 3/4ths of the
way around the drum (instead of half way as with normal VHS). These will
have the required alternating azimuth angles. This uses a 270 degree wrap
(the tape must wrap 3/4ths of the way around the drum as opposed to the normal
180 degree wrap for VHS).
(From: Andy Cuffe (baltimora@psu.edu).)
Beta camcorders used a half sized drum with what looks like one head (actually
2 heads very close together). It required a non-standard video signal from
the camera and used almost 360 degree wrap.
Indications of a bad video head include:
By the way - improper splicing of broken video tapes is a good way to break
video heads. Any kind of splicing should be avoided if at all possible.
(See the section: Recovering damaged or broken tapes.)
Note: in rare instances, similar symptoms are the result of a static brush
not making proper contact with the shaft of the spinning drum. See the
section: Firing (static) lines in picture during
playback.
An image where more or less good video alternates with snow at a 30 Hz rate
means that one of the 2 heads in a pair is probably either dirty or bad.
If your TV has a wide range vertical hold control (yeh, right, give me a
time machine), then you may be able to display both fields on the screen
at the same time.
The video heads may have picked up some oxide and are no longer making
proper contact with the tape. Letting the VCR play a newer tape for a few
minutes may clear this if it is minor. Otherwise, video head cleaning
(using the proper technique!) will be needed. However, seriously damaged or
improperly spliced tapes can result in serious damage requiring video head
(upper cylinder) replacement.
If your VCR has HiFi audio, similar symptoms may apply to the HiFi audio
heads on the rotating drum. Noisy or loss of HiFi audio or erratic
switching between linear and HiFi audio may be due to bad HiFi audio
heads (but could also be a tracking problem since HiFi audio tracking
can be even more critical than video tracking).
However, many other problems can result in similar symptoms - video head
diagnosis is one of the most difficult to make (except for physical damage).
Some pros claim to be able to determine if a video head is worn by feeling it
with a finger. I can guarantee that you will not be able to do this, so the
set of guidelines given above is the best to go on.
It depends on what's wrong with the picture. If you are getting "highlight
streaking in high luminance areas" (meaning that white objects in the picture
seem to have "tails" trailing off to the right of the object), then a new
head would help immensely. If there are random lines in the picture
(especially on tapes you have recently recorded on that machine), then a new
head will most likely help.
If the picture just isn't as sharp as the VCR next door, then a new head
probably won't help much. Technology has improved picture quality
considerably since your VCR was manufactured.
One recommendation - if you want the best picture quality from *any* VCR,
forget about recording programs in SLP or LP. The SLP (or EP) speed should
be banned and made illegal - the picture and audio quality are terrible. LP
should only be used on programs which exceed 2 hours. You should use SP
speed on everything you record if at all possible.
The HiFi audio is placed on the tape first to a depth of 4 microns. The video
head follows with video RF, which overwrites the audio to a depth of 1 micron.
Some of the original audio is erased, but 3 microns worth should still remain.
(This is why there can be interaction between audio and video on some HiFi
VCRs.)
A problem starts with head wear. As the head wears, the magnetic field it
generates actually increases. The video goes deeper than 1 micron, erasing
more of the HiFi audio. As the video goes deeper, tracking also becomes more
critical for the audio. However, self recordings should still have optimal
tracking assuming there isn't something wrong with the servo systems.
A temporary solution is to reduce the video record current, but this does not
replace the worn head material. The real solution is to replace the head drum
or buy a new VCR.
VCRs should be cleaned periodically, but video heads usually do not need
periodic cleaning as the spinning heads performs a self cleaning function.
If it ain't broke, don't fix it.
As noted below, there is a slight risk that at some point they may actually
destroy the video heads - no doubt timed to be 1 day after your warranty runs
out. In addition, they do nothing to clean those portions of the VCR that
really may need periodic maintenance like the rubber parts, A/C head, and tape
guides.
The only benefit of an automatic head cleaner is to the manufacturer of the
VCR as it increases their profit margins!
(Portions from: Joseph E. Fealkovich (jef812@ix.netcom.com).)
I would pull those 'automatic head cleaners' out and let the customer know
about it. I hate those things, they do more trouble than good. The least they
can do is redistribute the garbage back onto the heads, the worst, actually
catch on a head and tear it right out of the drum, (I've seen this happen on
a Goldstar VCR). When new, they do a fairly good job 'dusting' off the video
heads, but they wear out quickly, (they work every tape loading and unloading
cycle), and can seriously ruin the heads.
Furthermore, they clean only the video heads when they work; they do absolutely
nothing for the grooves cut into the drum, I'll say that's the most important
part, as the grooves form an 'air bearing', where the tape floats on the drum,
without that that effect, the heads can wear out prematurely due to the tape
sticking to the drum. My opinion on 'self cleaning' VCR's is, they've done just
about everything dumb and automatic on these VCR's.
Even if the tension is maintained (which is probably not the case), the
worst will be the same wear as an equivalent time in normal playing.
Most of the wear is from the spinning head-tape contact. Whether the
tape is moving at 0.3 ips or 100 ips is mostly irrelevant.
However, there will be additional wear of the roller guides and anything
else the tape contacts but even this shouldn't be a concern. I've never
heard of a VCR failing due to worn roller guide rollers. :)
Note that this approach is driven by the desire for rapid response, not
laziness on the part of the engineers. It is more difficult to design a
transport that performs FF and REW effectively while the tape is in the
loaded configuration.
Read the section: Video head cleaning technique
before breaking out the pliers and sandpaper (well almost).
(The following is from someone who not surprisingly would rather
remain anonymous).
My friend asked me to clean the heads on his VCR. I got out
my isopropyl alcohol spray (good) and my cotton buds (not good!).
I proceeded to scrub the upper drum furiously, getting lots of lovely
black deposits on the cotton buds. I, ahem... also scrubbed vigorously
around the four little 'recesses' positioned around the bottom of the
drum. When I spotted a little bit of metal sticking out of one of the
recesses, I got out my tweezers.....
(You can stop reading here if it's too painful!)
...and poked around, thinking 'this will cut the tape to ribbons if I
don't get it out'. After succeeding in removing the offending piece, I
noticed a very fine copper wire emerging from the hole too.... OUT IT
CAME (with the tweezers of course). I checked the other three holes
and succeeded in removing some more shrapnel from one other.
Guess what? It wouldn't play properly after this.... but the sound was OK.
To be fair, I was fairly sure I'd screwed up big time when I saw the copper
wire... but of course it was far too late by then.
I admitted to my friend that I thought I'd broken his video head and that
I would replace it for him. Thinking that heads cost around the $30 mark,
according to most of my catalogs, I was horrified when I got a price for
his particular model.... $162.00 + 17.5% tax and postage..... However, this
was much less than what the original manufacturer wanted: #350!! Well,
I finally found a replacement for $85. Still, an expensive lesson."
As noted, improper cleaning can destroy your video heads. The head chips
are very fragile and just rubbing them in the wrong direction (NEVER use an
up-and-down motion) can break the chips off requiring replacement of the
entire upper cylinder assembly - one of the most expensive parts in your VCR!
Manual cleaning using the proper head cleaning sticks is best but requires
that you gain access to the interior of your VCR - i.e., take off the cover.
If you do not want to do this, you can try a commercial wet cleaning tape.
These is some slight risk, however. The material used in some of these
may have an excessively coarse fiber structure which can catch a video head
and break it off. I have not seen this happen nor could I recommend a specific
brand as there is no way of knowing what their current product uses. I do
not recommend the dry type at all as these are almost always much more abrasive
and may cause premature wear of your video heads especially if used regularly.
When using the wet type cleaning tapes, follow the directions and - very
important - wait sufficient time for everything to dry out or else you will
have a tangled mess inside your VCR.
Regular video head cleaning should not be needed! Therefore, the regular
use of a cleaning tape is not recommended. As noted, some cleaning tapes
will cause excessive wear to the video heads and no cleaning type can
adequately deal with other parts of the tape path anyhow. If you find
yourself needing to clean your video heads frequently, the video heads may
be worn, the backtension may be set too high, or you may be playing old
or dirty (literally) rental tapes.
To clean by hand, you will need what are called 'head cleaning sticks'.
These are covered by chamois and are safest. DO NOT USE Q-TIPS (COTTON
SWABS). These can catch on the ferrite cores and damage them or leave
fibers stuck in the heads. Q-tips can be used for cleaning the other
parts like the rollers and audio/control head as described above but
not video heads.
To use the cleaning stick, moisten it with head cleaner or alcohol.
Pure isopropyl is best, however, the 91% medicinal stuff is OK as long
as you dry everything pretty quickly. Don't flood it as it will take
a long time to dry and you run the risk of any water in the alcohol
sitting on surfaces and resulting in rust (very unlikely, but don't
take the chance).
Gently hold the flat portion of the chamois against the upper cylinder
where it is joined to the lower (non-rotating) cylinder. Rotate the upper
cylinder be hand so that the heads brush up against the moist chamois. DO
NOT MOVE THE HEAD CLEANING STICK UP-AND-DOWN - you will break the fragile
ferrite of the heads - $$$$. Side-to-side is OK as long as you are gentle.
(The following tip from: Steve (sreed@amsupply.com).)
There is another advantage to this approach. The chamois sticks can on some
occasions "catch" on a video head, because the chamois area is small and
the edges are rigid. Using a larger cut-up square of chamois eliminates
this problem because the edges of the chamois are away from the rotating
head and you're simply holding it against the drum with your index finger."
I know people who use a piece of moistened typing paper, a business card,
Mr. Coffee filter paper - or even their Mark-1 thumb for video head cleaning
but I would not recommend these for a general service procedure at least until
you gain some experience with the use of chamois first!
(I suppose the only real requirement to prevent damage is that the material
have a fine enough structure and not have fibers that can get stuck in the
heads. So, the short list of acceptable materials is quite long - some more
effective than others. My concern for a general recommendation is that
people's interpretation of these requirements can vary quite a lot. If a
novice comes to me and asks what to use, I will say 'cleaning sticks'. Once
they understand the characteristics of the heads and their mounting, they are
free to use whatever works.)
Depending on how dirty your heads are, a couple of passes may be enough. Let
everything dry out for at least 1/2 hour. This may need to be repeated for
stubborn clogs. However, one pass will often do it. As noted, under NO
circumstances should you be going up and down even though you might think this
would work better given that the head gaps are vertical (or nearly so). Aside
from the possibility of breaking the head chips completely, there is no need.
The head gaps are solidly filled with a material of similar hardness to the
ferrite. Stuff can't get trapped in the gap - only on the surface, above
or below, and inside the winding area. Look at a head chip closeup under a
microscope sometime. :)
In addition, inspect and clean the drum itself staying safely away from the
video head chips. The five fine grooves in the drum help control the air
bearing that the tape rides on and helps to stabilize tape motion. These
should be clear of dirt and tape oxide (DO NOT use anything sharp - the
moistened head cleaning sticks will work).
As an alternative, I'd use a *dry* bit of paper. Moderate finger pressure
against the whole side of the drum, overlapping to the motor assembly. Then
twirl the drum in each direction a few times. Look at the paper and you'll
see exactly where the dirt is coming off. Once you can do this and get no
marks, you're heads are relatively clean. A tiny, soft, short brush and a
puff of air will dislodge any paper fibers. The paper and its fillers are
generally not going to harm the drum/ferrite-chips with this brief contact.
And you can pop a tape right in without waiting for solvents to evaporate.
Besides, solvents may soften any encapsulants on the chips, and cause residue
to get on the polished surface.
Once in a while, I run into a set of heads that seem to be bad, even after
cleaning with different methods. This is characterized by poor signal
strength in all or part of the picture, sometimes one field only, and
sometimes tracking range is extremely narrow as a result. On S-VHS units,
S-VHS recordings get noisy and may get blanked, while the same unit will work
in VHS with minor tracking problems.
Upon 30x pocket microscope inspection of the heads, I find a speck of what
appears to be a cloudy polymer, firmly bonded to the edge of one or more of
the chips. How did it get there? My guess: too much solvent - may have
dissolved encapsulant and/or dust that was at the edge of the chip.
Solution: *carefully* drag a jeweler's flat-blade screwdriver along the chip
(under magnification). Sounds a bit risky, but this has never damaged a head
in my hands. Follow this with a final paper-buffing, and usually the VCR is
tracking fine, with a much improved picture. Saves mucho bucks. 'Course,
sometimes the heads are just plain worn out.
My advice: Invest in a pocket microscope before you start pricing heads.
The normal MTBF (Mean Time Between Failure) rating for a standard VHS
video head is about 5,000 to 6,000 hours on the new machines. This figure
will vary from one manufacture to another, depending on the outcome of
their own research. This really means that after this amount of time
the head normally will be warn past its specs. This means that if you
look at the RF envelope on a scope, it will no longer meet the exact
specs for its output. it also will not be guaranteed to work anymore.
The actual life is really where it reaches the point where your playback
quality is considered unacceptable. This means it can probably last
about 10,000 hours in most cases.
What saves a head is that all the tapes used are of top quality, they
are not played in dirty or misaligned machines causing creasing of the
tape edges, or dirt transfer. The dirt or oxide stain from the tapes
can be a bit abrasive on the heads, thus accelerating some wear.
If the heads and tape path are kept clean, and high quality tapes are
used in the machine, you should reach a very high amount of hours with
the head.
I found that rental tapes are the worst for tape heads. This is
because many people play the tapes in dirty or misaligned machines,
and or handle the tapes with dirty hands from food.
I had one customer that played a rental tape in a machine, and it
started to become unstable during the playback. When I checked the
machine, I found peanut butter inside. It turned out that someone had
peanut butter on their hands when they handled the tape!
To check the signal from the video heads you need a circuit diagram so that
you can locate the relevant test points and expected voltage levels in the
head preamp. This will be housed in a metal enclosure, usually right next to
the head assembly (at the rear). This should be done with an alignment tape,
but any known good recording should provide a reasonable approximation.
Other basic checks such as visual check with a magnifying glass, continuity
tests on the heads as well as power supply voltages in the preamp can also
help.
If your VCR has 4 video heads (not including HiFi audio heads) and only
certain modes or speeds do not work, then the following procedure may permit
you to isolate the problem to a head or its preamp. Basically, the idea is to
interchange the wiring of the two pairs of heads. While the heads will no
longer be optimized properly for each mode, there is a good chance that they
will work well enough to determine gross changes. For example, if SP play
originally had alternating fields of good and bad video and works moderately
well after this rewiring (but maybe with tracking noise), then you know that
the bad head is no longer being used for SP play. Since the same head preamps
are being used, a bad head must be at fault. Video drums where the heads are
wired with flying leads are somewhat easier to cross-wire than those with a PC
board. This is not fun and may not work in all cases, but if you are hesitant
to risk the cost of a new head, it may be worth a try.
And, once you have looked at your 1000th bad head or so:
(From: Jerry Jansen (rjansen@bcpl.net).)
Try using a jewelers loop, along with a small pencil point flash light. The
diagonal formed into the chip is easy to see with the loop. As the chip wears,
you will see the angles length gets shorter.
(From: Raymond Carlsen (rrcc@u.washington.edu).)
There is (was?) a device to check for head wear by measuring the inductance
of the head itself. The head must be disconnected from the rotary transformer,
of course. Older machines had wires on top of the head that could be easily
disconnected (like the Beta decks) without removing it. Heads on some newer
machines must be removed from the VCR because the leads are underneath.
Apparently, the inductance of the head changes slightly as the ferrite
material wears away. The head gap itself doesn't change as the head wears.
If the gap were to open, the head wouldn't work at all, and I assume that the
inductance would be significantly different than a used good head. In most
cases, the head chip(s) wears to the point that the tip penetration is not
sufficient to keep it in intimate contact with the tape. The heads tend to
clog more easily as they approach end-of-life.
The inductance type of head tester does have a few drawbacks. It's rather
expensive, and to accurately tell how much usable life a head has left
using only the tester, you must have a "sample" of exactly the head under
test for comparison... each one is different. The measurement is relative,
not a "good-bad" reading.
However, I have been using several other methods to test video heads for the
last 10 years. Here are some options:
Different VCR brands will show different results to my finger test: Old
Hitachi decks will show bad heads before they actually "feel" worn out. One
usually goes first, producing alternating fields of snow and picture. I've
seen a few older Panasonics that still worked even when the heads were worn
down where they couldn't be felt any more.
How do you tell the difference between worn out heads and a head clog? Clean
the heads and try it again. Then feel it. Tentel Corporation makes a test
fixture that actually measures tip penetration, but with a bit of experience
as a guide, the best test instrument is still the mass of grey mud between
the ears.
When a repair job hits my bench, I use a combination of these methods to
evaluate whether a machine is worth fixing. If heads are close, I factor the
replacement cost into the estimate. I've only seen a few open heads (and rotary
transformers) over the years... quite rare. Loss of EP only can be that
both EP heads are clogged, but that's not likely if SP works well. Very
worn heads tend to clog more easily, but wear will be about equal for both
sets of heads. The only exception to that is HiFi machines where the high
fi sound gets bad before the picture shows up worn heads. If you suspect an
electronic fault, you might try making a recording in EP mode and playing
it back on another deck. If only the playback EP mode is bad, it's possibly
in the head amp switching circuit and not the heads themselves.
(From: Frank Fendley (frank.fendley@datacom.iglou.com).)
There are two methods (that I know of) which measure wear on video heads.
One is a protrusion gauge, which measures how far out the heads extend past
the edge of the drum. Once the heads fall below a minimum extrusion, they
are considered worn. It's similar to measuring the tread left on a
automobile tire.
The other is a "Video Head Tester", sold for either Beta or VHS models.
Essentially it is an inductance bridge. You connect each head to the test
leads, calibrate the unit, and then measure the inductance of the head. The
theory here is that as the head wears, its inductance goes down due to loss
of the core material. Past a certain minimum, the head is declared worn out.
Bear in mind that a head could fail both of the above tests and still give a
good quality picture (although it is true that its days are probably
numbered).
It is also quite possible that a head could pass either or both of the above
tests and be defective.
Are the the testers worth it? In my opinion - probably not, unless you are a
real purist and like to have a lot of test equipment.
(From Jerry Greenberg (jerryg@total.net).)
I researched out tip penetration specs on video heads for VHS and Beta (home)
machines. I got a number of people interested in this one to the point that
a few machines came off the shelf, and the research began. We had the tools
at our disposal to get this done.
The following measurements are in mm (millimeters).
Brand new heads off the shelf in both Beta and VHS were about 0.12 to 0.16 mm
penetration.
At about 0.05 mm the video signal starts to degrade. But the head will still
record well.
At about 0.02 mm the video is very noisy. If you loosen the head and push
it out a bit, you improve it slightly. But, the gap is now wider. Therefore,
the signal is a bit stronger (due to the additional penetration) but has more
noise. Overall, a slight improvement.
Also the horiz angle of the head effects the switch point a bit. If out, a
slight horizontal jitter (flag waving) is noticed, and the PG is slightly out.
You can correct with the PG adjust to a point, but the head effective angle
from the opposite one must be better than 2 deg.
As the head wears, we found that the head surface leaves the tape too soon,
and starts reading the tape too late. If the heads are down to about .05 mm
the effective error (both heads summed) is about 2 to 3 degrees. The
puts it slightly out of spec for the switch-over point and causes some
instability. This problem is also summed because the carrier output is at
about 60% of the normal amount. As the head wears from this point, the
carrier drops more rapidly. It is not linear. It follows the inverse
square law factor.
(From: Jaclyn (lambert@sos.net).)
The reason why it **appears** to be a record only problem is fairly
straightforward if you understand what's up.
When you make a recording with bad or marginal heads the resultant recording
is poor. Perhaps a vcr with good heads will be capable of producing an
"acceptable" picture, perhaps not. Depends on the alignment and how good those
heads are. When you try to play the "poor" recording back on the vcr in
question the resulting performance is unacceptable because the heads on that
vcr are marginal at best and are simply not going to have the gain required to
pull the crappy recording off. Get it? It's a double whammy two fold effect.
Video heads don't just go "bad". They wear down after time and early symptoms
sometimes also include poor vertical stability (as is so common in Hitachi
VCRs) and snow "lines" which hover about 2 inches from the top of the screen.
Occasional loss of horizontal sync is also typical.
Electronics suppliers such as MCM Eectronics, Premium Parts, and Dalbani
stock a wide range of video heads for VCRs that are more than a couple of years
old. (They may not have heads for the latest models.) In some cases,
they will offer two kinds of heads for the same model - a generic version
and a 'name brand'. Unless you are extremely critical, there is probably
no need to spend the extra on the 'name brand' head. There is also no need
to pay the premium charged by the original manufacturer of your VCR - it is
often priced 2:1 or more over what a generic head will cost with no
substantial difference in performance, if any. You may even end up with
exactly the same head manufactured on the same assembly line!
Note that currently, the price of many upper cylinders (video heads) for
2 head VCRs is well under $25 so ordering a replacement may be a better
investment of time and effort than a long diagnostic procedure especially
if the old head has high mileage and video quality has been steadily
decreasing.
Unless you can find a junk VCR (try Allbrand, see the section:
Used VCR parts), repair may be too expensive.
Just buy a different brand next time, which, of course, may not matter. :-(
CAUTION: Make sure ALL connections are actually freed from the PCB before
attempting to remove the old head. Use a pair of needle-nose pliers or
other suitable tool to separate the wire from any residual solder.
Otherwise, it may rip off parts of the rotating transformer assembly,
possibly ruining the entire cylinder unit.
In rare cases where there are individual wires, a generic replacement
head may not be color coded the same or have the wires originating from
different places than the original. In this case, you will have to try
to determine which physical head chip the wires originally connect to. You
must get each of the connections from the lower cylinder to the head in the
same physical head as before (though the polarity or phase of the pair of
connections to each head should not matter).
Do not yank or pull hard. The head should come off easily. If it does
not, make sure the solder connections have been completely removed. See
CAUTION above.
If the tracking is now way off or you experience serious video noise,
lack of or erratic color, or bad or missing HiFi sound, refer to your
diagram and double check that you didn't replace the head rotated 180
degrees from the proper position by accident. Make sure the drum is seated
properly - not on a bit of dirt on one side. DO NOT be tempted to adjust
tape path alignment - if the heads were the problem, it should be fine.
Also see the section: HiFi/video tracking problems
after upper cylinder replacement.
It is a good idea, however, to perform what is known as the 'Tape
Interchangeability Adjustment' (this terminology is used in Panasonic
VCR service manuals, meaning is self evident) in any case. This procedure
consists of adjustments to the roller guides, other guide posts, and the
A/C head. See the chapter "Tape Path Alignment and Backtension Adjustment"
or follow the set of steps in your service manual. On rare occasions, some
electronic adjustments will also be required to obtain optimum video
quality but this is the exception rather than the rule. Tapes recorded
at EP speed will almost always be more finicky and may require these
adjustments more so than those recorded at SP speed.
If it's a Samsung based machine, you might need a head puller. I got one at
a service seminar many years ago and need it once in a great while to pull
a stubborn one, usually a Samsung. Avoid the temptation to pry up with
screwdrivers. I've seen the results of such abuse... not pretty. Look for
threaded holes in the head drum. That's a clue it needs a puller, which
attaches to the head drum and presses downward on the center spindle with a
few twists of the handle. The new head (also a tight fit) is seated by
alternately tightening the two mounting screws.
You could make a puller with a bar of metal and some long screws. Drill two
holes in the bar to fit the spacing of the threaded holes in the head wheel
and one in the center between the other two. Tap the center hole (8-32 is big
enough). Use screws (small metric) long enough to thread into the drum to
attach the bar. Run a screw down the center hole until it contacts the center
shaft of the drum. Keep rotating until the drum pulls off.
When replacing the upper cylinder, the orientation and wiring must be exactly
the same as the original. For many VCRs, this is automatic since the mounting
is keyed and the wiring is via direct printed circuit board connections.
However, there are also many where it is possible to screw up either the
orientation or wiring or both:
(From: John R. Hepburn (jhepburn@recorder.ca).)
If you have an oscilloscope and service manual, check the envelopes for
maximum output. Audio and video should max at roughly the same tracking
position. If they do, forget about heads or any mechanical problems, it is
electronic (but probably existed before the replacement - possibly masked by
an originally defective set of heads!).
If they do not, then it is probably a drum problem. DO NOT adjust your
roller guide height or any other posts! They were in the right position
before (unless you have already moved them) so they are in the right position
now. Minor post adjustments are OK after heads are replaced, but that is just
to peak it out. No serious problem has ever been solved on a VCR by adjusting
posts that are in their original position. Remove the heads and check for
proper seating. You would hate to make a big deal out of this, only to find one
side of the drum was seated on a small piece of residue.
You should be using the test tape that has both the standard video on
it and the HiFi envelope as well. The lateral alignment of the
control track head is extremely critical, and should be done along
with the guide alignment.
Also the head switching pulse should be checked closely. In some
machines the switching pulse is not adjustable. If this is the case,
you should be using the original factory replacement head for sure
(not a cheaper sub). The universal replacement ones have given me a
lot of trouble...
As for the slow speed, there is no real test standard. The slow heads
should be accurately aligned from the factory on the drum to match.
You cannot adjust the slow speed separately for the tracking. On
some very high end machines, especially the older ones, they had a
separate head switching adjustment for the slow speed...
(From: John F. Reeves (jreeves@uwf.edu).)
Take an alignment video-cassette tape and verify that the P2 and P3 posts
are adjusted properly. you should use a scope and monitor the RF envelope
while adjusting the above mentioned posts. Once this procedure is done,
make a recording and play it back in another VCR. If it still does not
track properly, it may necessary to perform the tape interchange ability
adjustment. This adjustment in more critical and more in depth, should be
performed be a qualified technician.
First confirm that it is even possible to do this - some are keyed in such
a way that a hammer would be needed.
The effects will depend very strongly on the particular VCR but the following
are among the possible symptoms:
For really major tracking problems with all tapes, check for broken or
missing parts or for problems which prevent proper positioning of the roller
guide assemblies during tape loading. Types of symptoms include: broken
up picture, snow across part of picture, multiple breaks (sort of like the
VCR is in a search mode such as CUE or REV but is not) in picture, totally
unstable picture, or multiple of the above. Of course, someone before you
may have messed with various mechanical (or heaven forbid, electrical)
adjustments without having a clue of what they were doing.
Before you try to adjust the A/C head, make sure that there is not some
obvious mechanical problem that has shifted its position. There may be a
bit of something stuck in the mechanism. If this appeared after you did
some work on the VCR, you may have accidentally caught a cable or something
else preventing the A/C head assembly from returning to its proper position.
This is particularly likely if the problem happened suddenly.
Once you change its settings, any tapes recorded on your VCR prior to these
adjustments may not play back properly. For example, if you touch the A/C
azimuth screw to correct a muddy weak sound problem when playing tapes from
other VCRs, any tapes previously recorded on your VCR will now sound muddy
and weak. You need to decide which is more important - your recorded tape
library or compatibility with other VCRs.
Before you try to adjust the roller guide height, make sure that there
is not some obvious mechanical problem which is preventing the roller guides
from seating properly. This is particularly likely if the problems
happened suddenly. See the section below on: "Likely causes for sudden
change in tracking behavior".
Gently check each roller guide to see if one is loose in its threaded mount.
If one turns with finger force, that one is likely the problem AND YOU SHOULD
NOT TOUCH THE OTHER ONE! Where both are loose or have been adjusted, it may
take quite a bit of trial and error to get them both set correctly again.
Try not to make this an issue!
Considering the precision required to maintain alignment, especially for the
slow (SLP/EP) speed, it's a wonder these things work at all! With a track
pitch of 19 um (.019 mm) at this speed, a shift by more than the diameter of
a human red blood cell (about 7 um) will result in alignment problems.
Tolerances of SP and LP speeds aren't quite as bad but are still measured in
almost imperceptible fractions of a mm.
Changes in roller guide height is probably the one most likely to occur. Note
that many modern VCRs no longer use locking screws so these do eventually
loosen and shift position. Wear to other parts like the V-stoppers and tracks
on which the roller guides ride, as well as the ridge on the lower cylinder,
are also possible.
However, before attempting realignment or replacing expensive components, make
sure that the roller guides are seating properly and that a proper cleaning
and inspection has already been done.
You may need a special screwdriver with a cutout in the middle of its blade
(or modify one of your own) to easily adjust this nut.
Note: For the procedure below, the linear audio tracks must be monitored. So,
if this is a HiFi VCR, select an audio mode that forces the linear audio
tracks to be used as output. There will usually be a switch or menu setting
for this.
The following will attempt to get your mechanical settings back to something
approaching normal even if the audio/control head was tweaked:
I assume that you have cleaned it and replaced any dead rubber parts.
I also assume that someone (we won't name anyone) has tweaked just about
every mechanical adjustment.
I would adjust the audio/control (A/C) head as best you can (don't touch this
unless you know it was messed up by someone):
If you are aligning a HiFi VCR, (re)enable HiFi mode and tweak the mechanical
tracking to center both video and audio within the electronic tracking range.
In some cases (if the rotating video/audio heads were not manufactured
perfectly), the peaks may be at slightly different positions and you will
have to split the difference in the adjustment.
There can still be other problems in the tape path including the height
and angle of the roller guides and the height of the impedance roller
assembly (on the left before or after the full erase head.)
Also, have you touched any other mechanical adjustments - other guideposts,
etc? Hope not. Also, I assume that any repairs to the guideposts have left
them perfectly vertical - if they are tilted, then other tape path
instabilities can result.
The following checks and adjustments are made in PLAY mode.
There is a ridge on the lower (stationary cylinder) on which the tape should
ride - not above and not below. Play a tape that is in good condition
and look closely at its bottom edge to see if it is sitting precisely on
this ridge. If it is not, first verify that both roller guides
are snug against the 'V-Stoppers' - the brackets at the end of the
tracks where the roller guides stop in PLAY and REC. If they are not,
then you need to determine what is binding or what has fallen off of the
tape loading mechanism. See the section: General tape
path alignment problems. Assuming that the roller guides are correctly
positioned on the tracks, the first step is to visually adjust the roller
guides so that the tape just rides on that ridge on the lower cylinder.
That ridge is a very critical part of the guide mechanism.
There will be a set screw to lock each of the roller guideposts from turning.
The appropriate one(s) will need to be loosened slightly - just enough to
that the post is snug but can be turned by hand. The set screws may require
a miniature metric hex wrench. Some just have a square head screw which
can be loosened with a pair of needlenose pliers. Adjust each guidepost so
that the tape just rides on top of the ridge.
Now, for the fine adjustments. Which part of the picture is bad?
Misadjustment can also cause a periodic loss of sync on a several second cycle.
Make careful **small** adjustments of each one - then wait for a few seconds
for any results to become apparent. Since the tape moves so slowly,
it takes several seconds for the tape motion to stabilize to the new
guide position. The left guide will affect the top part of the picture
(mostly) and the right guide will affect the bottom.
Once you are happy with SP, get a tape recorded on a known good deck in
EP (SLP) mode since the tracks are narrower and fine tune it.
Tape path alignment comments:
Roller guide tilt: The roller guides (but not the fixed guide posts next to
them) should be perfectly vertical. Sometimes there is an adjustment for
this but usually not. Roller guide assemblies that have tilt due to wear
will need to be replaced.
Mostly, these symptoms are related to problems with the roller guide
assemblies. (though electronic causes are also possible). The roller
guides are on the assemblies that move on curved tracks to wrap the
tape around the video head drum in play and record modes (and on newer
instant start VCRs, other times as well). Each roller guide assembly
includes a white cylindrical roller which should turn freely on a metal
guidepost, and a fixed guidepost at approximately a 20 degree angle.
For the JVC problems, the parts are usually either a brass post or a
plastic link. The brass post can be glued back in place using a drop
of Epoxy. Make sure its shoulder is fully flush with the body of the
roller guide casting. For the plastic link, I have used a very small
screw to secure it in place from above. Some plastic cement may
work as well.
Check the roller guides while the machine is playing a tape. They should be
firming pressed against the V-Stoppers. Any looseness indicates a problem
preventing full engagement. If pushing the offending guide into position
fixes the tracking problem, this confirms the diagnosis.
Note that in modes where the roller guides are retracted, the roller guide
assemblies are relatively loose and free to move. However, the amount
of movement possible should be similar for the left and right roller guides
and you should not be able to lift either entirely off of the track - the
ability to do so means missing parts underneath the deck. If the missing parts
can be located, they can usually be glued back into position.
Warning: if you find a roller guide assembly that can be lifted off the
track DO NOT attempt to load a tape - the floppy roller guide assembly
can smash into the spinning video heads ruining them - and your entire day.
If the backtension is too low, poor tape-head drum contact results and
you get a noisy intermittent picture.
If the backtension is too high, there will be excessive head wear and in
extreme cases, the drum will slow or stop entirely.
Backtension is normally set using a special backtension gauge which you
most likely do not have. If you own a TV with a vertical hold control,
you can adjust backtension by setting the vertical hold so that you can
view the head switching point - just above the vertical blanking bar.
Above this point, you see the video from one head and below you see it from
the other. When properly adjusted, these two segments should more-or-less
line up.
There are two adjustments for backtension: a spring position and the effective
length of the band.
To set the length, there is a setscrew which allows the end of the band to be
moved back and forth. It is unlikely that you would need to set this unless
you have just replaced a band or unmucked someone else's repair attempt.
I usually consider the length to be correct when the angle that the tape
makes going around the lever post is about 90-120 degrees. In other words,
the tape should not be so tight as to not be deflected by the arm but
should not be so loose as to be near or at the end of its possible travel.
Then, set the spring force to align the picture above and below the head
switching point. If you do not have access to vertical hold, you may be able
to set backtension in the middle of the range where flag waving (see the
section: Flag waving - top portion of picture wiggling
back and forth) is absent or minimized.
Well, I'm about to open myself up to all sorts of scathing comments, but here
goes: You can get by without a back tension meter. You will notice that just
about every VCR ever made puts the back tension pole between a post and the
impedance roller. Adjust the pole landing position so that it lines up with
the middle of the impedance roller. Check your picture. If you have flagging
at the top, or wavy lines, adjust the position. Fiddle it both ways to get the
feel of it. Once you have experience, you can gauge the back tension by
holding a screwdriver against the tape after it has passed over the full erase
head. Your fingers are probably more accurate than most gauges anyway - I've
never seen two give the same readings. My meter lies unused most of the time.
I've lost count of the number of times I have chased around the VCR only to
find my backtension meter was leading me astray.
The objective of the back tension adjustment is to prevent "flagging"
which is horizontal displacement of scan lines at the top of the picture.
You can use either B&W or color TV (or video monitor), provided that the
unit has an accessible vertical hold (vertical sync) adjustment. You
mis-adjust it until the picture rolls half-way and you can see the
horizontal sync bar. This lets you see the very top of the picture (just
below the bar).
To make the adjustment, you need a known-good reference tape. You might
trust a commercially-produced movie, but I'd recommend a real vcr
alignment tape if you can find one. If you use a movie, then try four or
five different ones to help insure you don't have one made on a defective
machine. Adjust your machine so that vertical lines in the very top of
the picture are as straight as possible.
As to the specifics of what to adjust on your machine: You didn't mention
the make or format of your machine, but I'll wager that the moving arm
nearest the feed reel is attached to a felt-covered metal band (the brake)
that wraps partially around the feed reel table. With tape loaded and
moving, the arm balances tape tension applied by the drive system against
tension supplied by a spring. If the tape tension becomes excessive, the
brake is applied more; if the tape loosens, the brake is relaxed. Look at
the attachment points for the spring attached to the arm. Usually, the
back tension adjustment is at the chassis end of the spring. It may be an
eccentric post than can be turned with a screw driver or a special tool,
or it may be that you have to gently bend the tab. Either way, adjust the
spring tension in very small increments, then observe the effect on the
picture.
The light source can fail - this is common on older VCRs where this
was an incandescent lamp but rare on modern VCRs which use a special IR
LED. The failure of this light source can produce a number of symptoms:
If your VCR uses an incandescent lamp and it is not lit when power is on,
then the bulb is most likely burnt out.
If either sensor fails open, then similar symptoms may result.
If the sensor on the supply side fails shorted, then it will appear as
though the tape is at the end. The VCR may refuse to play or FF or will
attempt to rewind as soon as a cassette is inserted.
If the sensor on the takeup side fails shorted, then it will appear as
though the tape is at the beginning. The VCR may refuse to REW.
In both cases, sometimes you can trick the VCR into cooperating and
confirming that there is a sensor problem by pulling the connector
for the appropriate sensor once the cassette is loaded.
If you can get at the connectors, you can test the sensors by monitoring
the voltage on the outputs.
One test you might try if the VCR attempts to play an imaginary pre-recorded
tape as soon as power is turned on is to locate the microswitch for record
lockout protection - it will be located near the front (where the record
protect tab would be once the cassette is loaded). Press this in while you
turn power on. If the VCR now just initializes and displays cassette-in
without trying to play, then it really thinks there is a cassette in place
most likely due to a faulty sensor.
In some cases, there could be other problems like a faulty mode switch
or microcontroller producing symptoms that might be mistaken for faulty
start/end sensors.
You can also try powering the LED with a low voltage supply and 500 ohm or
so resistor using the IR detector to see if it works. Disconnect it from
the circuitry first! Try both polarities to be sure you got it right.
The sensors themselves can be tested by disconnecting them from the
circuitry and shining an IR source on them (a remote control or
incandescent bulb) while monitoring the resistance with a VOM or DMM.
Use the polarity which give the higher reading (reverse bias). This
resistance should drop dramatically if they are functional.
If the start and end sensor assemblies are interchangeable, swapping them
may be instructive. For example, this may shift the symptoms from play to
rewind or vice versa.
What I call a reference counter is what all VCRs used up until a few years
ago. A sensor counts revolutions of the takeup reel (usually) either
directly or via a belt drive. A mechanical or electronic counter displays
an arbitrary number which provides some idea of location. Since the
rotation rate of the reel is not constant with respect to the actual
time of the tape, it is not possible to use this for anything other than
a reference. In addition, the tape may slip a bit and be wound tighter
or looser depending on whether it was wound in play, FF, or REW. Thus,
even the reference is not accurately repeatable.
Failures can be caused by a broken or weak belt for the mechanically
operated counter or defective circuitry for the electronic display. A
failed sensor would most likely also cause the VCR to shut down and
unload the tape as this is what is used to confirm that the takeup reel
is rotating and that tape is not spilling into the bowels of the VCR.
Real-time counters - which really are a vast improvement - operate off
of the control track pulses from the control head. Tape location is
measured in hours, minutes, and seconds though it is still relative
and must be reset at the beginning of the tape if an absolute location
is to be determined.
The only disadvantages of real-time counters are that:
Failure of the real-time counter on a VCR that otherwise works normally
is quite unlikely and is probably an electronic problem since the
control head must be functional for all record/play modes to work properly.
However, it is possible that a failure of a half loading arm to fully
extract the tape would result in problems in (non-search) FF or REW.
Failure of this sensor will cause the machine to shutdown almost immediately
and will result in a stuck tape counter.
If your VCR has identical sensors monitoring both reels, swapping the sensor
assemblies may be instructive: the behavior will change if one is bad. For
example, a VCR that would shut down in a couple of seconds in play mode may
continue to operate correctly but now have problems with rewind.
Note that on VCRs with real-time counters, the real-time display as well
as possibly the tape movement sensing operates off of the A/C head control
pulses. Failure here could be due to dirt, a bad A/C head, tape path
alignment problems, or failure of a half loading arm to properly extract
the tape so that it contacts the A/C head.
For electrical tests, first, locate the LED and photodiode. You can tell
the difference by testing with a DMM on its diode test scale - the LED will
have the higher forward voltage drop. Sometimes, the connections are even
marked. What a concept!
Momentarily touch and remove a resistor (1K ohms or so should work) across
the sensor leads (while the VCR is in PLAY mode before it quits if needed).
This should make the counter change if the the LED is bad or the photodiode
is open. Alternately, a remote control may be able to activate it providing
pulses that will look to the counter exactly like reel rotation.
If this has no effect, unsolder the sensor (or unplug the sensor assembly
from the main board if there is a connector) and try the resistor across
the terminals where it was connected. If you now get a response, the
sensor was shorted (or the connection was bad).
If you do not get the counter to change in either case, there is a problem
with an intermediate buffer amplifier, the electronics on the main board, or
a bad connection leading to the main board. You will need to obtain the
service manual or trace the circuit leading to where the sensor signal is
detected.
It is possible that the counter will only change when the microcomputer expects
the reel to be moving, so a test while in STOP mode may not be valid.
An alternative test is to use an ohmmeter across the photodiode on a high
ohms scale. Use the polarity which gives the higher resistance and shine
a light on the sensor. The resistance should drop dramatically with a bright
incandescent light (these put out a good amount of IR). If it is infinite
in both directions, the photodiode is open. If it is low in both directions,
it is shorted. You may be able to make a measurement while the sensor is
still in circuit, though other components may mask the resistance change.
As noted, the IR sensor/LED combination is often a pluggable assembly.
Using my VOM on a photosensor, I read infinite ohms with no light and 200 ohms
with a bright light. However, your mileage may vary.
If you have an oscilloscope, monitor the sensor output. If it is a voltage
signal at this point (likely), then you should see it go high and low as you
rotate the reel or shine light on it. With the reel rotation, the low and
high periods should be roughly equal. There may be a buffer amplifier driven
by the sensor - check its output as well. The signal there should be a
cleaned up version (low pass filtered and possibly inverted) of the sensor
output. In all cases, the signal should be a DC value without noticeable
ripple or noise (block external light as fluorescent lamps in particular may
add a 120 Hz ripple to your detected signal). Even at transitions between
low and high or high and low, the level should change smoothly. You may
be able to trace the signal to its final destination, the microcontroller
or other large multilegged part, and monitor it there as well.
Play a T120 tape recorded at EP speed near the end of the tape. This will
result in the slowest takeup reel rotation. Or, if your VCR has the counter
active in stop mode with the cassette out, rotate the takeup reel by hand
very slowly.
If the counter skips or 'free runs' at certain positions of the reel, there
may be a problem with the hysteresis circuit. If this is external to the
microcontroller, a resistor may have opened or there may be some other easily
identified bad component. If it is internal to the microcontroller - either
an actual circuit or firmware - then replacing the microcontroller may be
the best solution unless you want to add your own circuit - I have done this
to repair a Sears VCR with an erratic counter problem. It is a simple 1 or 2
transistor circuit (depending on what external circuits are already present).
Monitor the sensor output when rewinding a T120 tape to the very end - this
will be the worst case test as the pulses will be at the highest rate. There
should be no missing pulses and the high and low times should still be similar.
A bad sensor might result in unequal high and low times and dropped pulses
at high speed.
Try removing the take-up reel disk. Look on the bottom surface to see if
there are a series of pie-shaped vanes - shiny, dark, shiny, dark, etc. If
the shiny vanes get misted with smoke or general grak, the symptom is the
same as if the sensor itself is faulty. Use some Windex or some such mild
cleaner on the vanes and test the machine again.
On some earlier machines, the take-reel disk might have a series of evenly
spaced slots - blank,solid,blank,solid etc.-that interrupt the flow of IR
light creating an electronic pulse stream. If your machine has this type
of motion sensor, you can try brushing or blowing out the dust that may
have accumulated in the small recesses surrounding the IR emitter and
receiver devices on the sensor assembly.
If these attempts don't do the trick, you probably have a faulty sensor.
The video head drum (3) always has its own motor. It is internal to
the lower cylinder or above the upper cylinder (except in the very
oldest VCRs) and directly drives the spinning upper cylinder.
Most consumer VCRs use a single motor for the capstan and the takeup
and supply reels. Some also use this same motor for cassette and/or tape
loading. Several possible types of small motors are typically used in VCRs:
The following are some of the possible problems that can occur with the basic
permanent magnet motors:
An open or shorted winding may result in a 'bad spot' - a position at which
the motor may get stuck. Rotate the motor by hand a quarter turn and
try it again. If it runs now either for a fraction of a turn or behaves
normally, then replacement will probably be needed since it will get stuck
at the same point at some point in the future. Check it with an ohmmeter.
There should be a periodic variation in resistance as the rotor is turned
having several cycles per revolution determined by the number of commutator
segments used. Any extremely low reading may indicate a shorted winding.
An unusually high reading may indicate an open winding or dirty commutator.
Cleaning may help a motor with an open or short or dead spot but most likely
it will need to be replaced. Note that unlike a CD player which uses
some motors constantly, the small PM motors in VCRs are only used for loading
operations and are generally quite reliable unless damaged by other problems.
For more information on small PM motors, see the chapter: "Motors 101" in the
document: Notes on the Troubleshooting and Repair of Small
Household Appliances and Power Tools.
Some Sony VCRs have had problems with defective capstan motors resulting
in intermittent pausing or stopping of video playback when hot. The entire
motor or just the bearing assembly needs to be replaced in this case.
VCR capstan motors are servo-controlled to allow precise speed and phase
control. Typical signals are:
There will probably be other connections for a variety of servo voltages,
braking, grounds, etc. - You may need to find service literature for this VCR
or the datasheet for the particular driver chip to get more info. Data will
also tell if motor is 3-phase. This is common for many capstan motors and
would require this IC to run it.
However, whether from wear and tear, or even if the technician doing the
setup in the VCR factory had an off day, this distance may not be quite
identical on the VCR that the tape was recorded on and the machine being used
for playback. Therefore, a way is needed to adjust the effective distance.
A mechanical control would be possible but not very elegant. Therefore, an
electronic tracking control is provided. This basically allows adjustment
of the time delay or phase of the control pulses from the control head during
playback. Record tracking is fixed. Actually, there may be as many
as three tracking controls: (1) the user tracking knob or buttons, (2) an
internal master tracking adjustment, and in fancier models, (3) an
autotracking servo system. (Note: tracking is always automatically reset
to the default when a cassette is inserted.)
Another set of heads is required for HiFi audio.
The only possible difference for record or at normal playback speeds is in
picture quality since with 4 or more heads, head widths/gaps can be better
optimized for each speed. For example, a wide track width can be used at SP
speed and a narrower one for EP speed. Which VCRs do this, I have no idea.
In fact, such differences might only be visible to the average viewer in an
A/B comparison under controlled conditions.
The stability of the video playback has nothing to do with the number of
heads. A jumping picture during playback is due to a servo system problem.
With problems of this type particularly on a new VCR commercially recorded or
rental tapes, it is more likely that the VCR is having problems with some kind
of copy protection scheme.
For a 4 head VCR, this may even include all 4 at once. In this case, signals
from both heads of the pair on each side of the drum are monitored and the one
with the greatest amplitude is sent to the video circuitry. This provides
clearer special effects for SP recorded tapes in particular - CUE, REV, SLOW,
and PAUSE - where the video heads may be crossing tracks of both azimuth
angles. Such an approach may be called a 'double azimuth' design by the
manufacturer.
For record and play modes, an opposing pair will be used but which pair will
depend on speed - EP, LP, SP.
Thus, almost anything is possible and it gets to be confusing very quickly!
Don't count on finding this information in the service manual either.
A six head (VHS) vcr has 4 video heads and 2 audio heads on its rotating
upper cylinder. The 2 audio heads record VHS Hi-Fi. They are about 1/3 the
width of the most narrow video heads (about 6 microns). A four head
machine lacks the audio heads and is therefore incapable of playing or
recording Hi-Fi. There are also 2 head machines on the market. They use
the same pair of video heads for all tape speeds. 4 and 6 head machines
use the 28 micron wide heads for SP (highest speed), and the 19 micron
heads for LP (middle) and EP or SLP (slowest) speed. Some machines have a
7th head: the flying erase head. It is about 40 microns wide, and when
activated, can erase the recorded tracks of both video fields that make up
a frame. Most vcrs use all 4 video heads to smooth out the picture when
scanning in fast forward and rewind. This is why 2 head machines have
much more noise in the picture when scanning.
Machines that have a switch to turn off the 19 micron heads do so in an
attempt to improve the playback of tapes made on old 2-speed (SP and LP)
machines. These machine had video heads that were something like 22
microns wide, and scanning them the narrower heads of a modern machine
sometimes produces unacceptable results.
Compatibility problems between machines are a fact of life because of
mechanical differences. Recording at the highest possible speed minimizes
problems, but hi-fi audio tracking problems can happen even then because
the tracks are so narrow. If you have video tracking problems between 4
and 6 head machines on tapes recorded at the highest speed, it is because
of mechanical differences, not because of the number of heads on the
machine; the number of video heads is identical. The differences are in
the alignment of the audio/control head that controls synchronization of
the video upper cylinder, and in alignment of the video heads themselves.
Since few people have SVHS decks, there is probably little benefit if the
objective to to make high quality recordings to share.
I would probably go with a good 6 head (including 2 HiFi) since it will be
compatible with everyone.
However, just saying it has 4 or 6 or 25 heads doesn't mean it will produce
a high quality result - there is a lot of variation in video and to some
extent HiFi audio quality.
(From: Ed Ellers (kd4awq@iname.com).)
VISS is a real standard, issued by JVC in 1986. There is also a VASS -- VHS
Address Search System -- using the same techniques, but it was taken off the
market in 1988 after a patent infringement suit by a German company; JVC
settled that case, but VASS never came back (at least not in North America);
JVC later developed a more sophisticated system called CTL Coding, but it's
not used on consumer VCRs over here either. VASS records four-digit codes
instead of a single index mark; CTL coding records an actual time code on
the control track, and also provides for VISS and VASS use.
Incidentally, VISS and VASS work by altering the duty cycle of the 29.97 Hz
square wave recorded on the control track; the servos still work on the
average phase of the signal, but the changes in duty cycle are decoded into
a slow bit stream. Before VISS was developed a number of VHS VCRs had a
different indexing system that recorded a low-frequency signal across the
entire tape, using a special head on an arm that contacted the tape while it
was rewound into the cassette; these index codes could only be placed at the
beginning of a recording and couldn't (then) be read except during rewind
and fast forward modes. Theoretically a modern VCR could be made to read
this signal using the control head, but this would require a special circuit
to be added; I don't know of any VISS-capable decks that can do this, and
given the small number of recordings likely to still exist with the old
index signal it wouldn't seem to be worth the trouble.
My understanding of commercial advance is that the program is monitored
during recording for fade to black and silent audio between programming and
commercials and between commercials. The microprocessor stores these events
in memory until the recording session is over. It then analyzes these
events to determine whether an event was part of a group of commercials or
just a dark silent passage of programming. The tape is then rewound and the
beginning and end of the commercial groups are marked with special start and
end signals recorded on the control track, similar to index search marks.
During playback with the feature activated the unit will automatically
forward search when a start signal is detected and resume normal play when
an end signal is detected.
On the other hand, I had to repair my high-end (for 1990) moderately used
Mitsubishi VCR because a 10 cent plastic part broke (their cost, my
cost - $10) - clearly an exercise in design-to-fail engineering. For
about 0.5 cents more, it could have been built never to fail. The
replacement part was identical to the original, so I give it about 4 years.
In recent years, the rapid decline in the quality of construction of VCR's
has been widely chronicled here and in other forums. Through all of this
criticism, I have staunchly defended JVC as the last bastion of construction
integrity! Alas - no more!
Tonight, I had the occasion to open up a JVC HR-J620U and was shocked at what
I saw! I am sad to announce that even the once venerable JVC has sold out to
the concept of making machines really light and really, really crummy! This
new JVC transport is the epitome of designing "throw away" machines - even
worse than the transports offered by Matsushita or Funai! Glaringly absent
is the modular power supply. You may no longer fall back on the last resort -
replace the power supply! Folks, this is just an unmitigated piece of
unadultered crap!
As both a consumer and a VCR technician, I am truly offended by the shoddy
construction of all new VCR transports and, in particular, by the caving in
of JVC to make machines geared to the lowest common denominator. All of us
should be outraged!
(From: Greg Monbourquette (gregm@globalserve.net).)
I too am concerned about the lack of care that the engineers who put these
things together take when considering the amount disassembly required in order
to only clean a lousy belt. (I'm talking mostly about the RCA/GE models with
a plastic plate covering the bottom of the VCR) And yes there was once a time
when you could buy/sell a vcr and KNOW that the customer won't have any
problems for at least 5 years . I tell my customers all the time when they
finally decide that the 15 year old TV that finally died ( for the first time)
will be replaced by a new one, " don't expect 15 years out of any TV you buy
today. Oh well we've (I've) ranted long enough. I now know my feelings
aren't only mine.
(From: CLSNOWYOWL (clsnowyowl@aol.com).)
I have been doing repair for 15 years and I can actually tell you that during
my career as a technician, I have actually seen the actual quality get worse
over time on all electronics devices, including VCR's for three basic reasons:
In today's devices, I see brittle plastic gears that actually break just
from use and I can actually bend the metal in the devices with my bare
fingers, if I apply any real force at all.
The newer type tuners actually will only display a channel if a picture
actually comes in clearly. If the channel barely comes in or comes in even
fairly decently, you get a blue screen.
Today's devices use components with very strict electrical tolerances of say
plus or minus one to three percent (1-3%), which means that in the newer
devices, the likelihood of a failure is anywhere between 67%-90% more
likely.
It is clear that I have more margin of error on an electronic components from
plus or minus 10% or even plus or minus five percent than I do with a component
that has a plus or minus 1 to 3%.
So, for these three reasons, the overall quality of the actual manufacture of
new electronics devices has gotten significantly worse than a device made
back in 1990 or before.
All S-Video means is (1) a special connector and (2) separate luminance (Y)
and chrominance (C) rather than composite video.
In a VCR, you will need to bypass the input circuitry and get to the place
where Y and C are separate. This may or may not be possible depending
on its design.
It is probably not worth it as you will likely not gain much in picture
quality but if you really are determined, a schematic will be essential.
If all you want to do is allow for an S-video input, there are single
chips which will combine the Y and C into a normal composite video
signal.
However, there are a couple of problems with attempting to cleaning record
single frames on a consumer grade VCR:
Other than that, there is no reason that the video writing circuitry
cannot be turned on during pause - some VCRs will do this if you
go into record mode while in pause.
Obviously, anything you can do from the front panel or remote you can
do under computer control. There could be hidden functions accessible
via a special connector or key sequence but you would need documentation
for your unit which may not be readily available, if at all.
(From: Bill Mohler (bill@cs.oberlin.edu).)
We did a project to control multiple VHS VCRs where time and cost
were major factors. Our VCR's were the same brand (assorted models with
same IR codes), so we hacked a remote to interface to a PC's parallel port.
The basic idea was to have the PC select a VCR then "push" a button for
function.
The remote hack was simply an analog switch (TTL input) across the switch
contacts and a 754XX peripheral driver to select an IR LED mounted right
in front of each VCR's IR window.
The software was simple. We only needed 4 VCR's and 4 functions, so we
split the 8-bit printer output into two 4-bit commands ("VCR select" and
"function") and "poked" away. Not bad for a days work.
You could use decoders or the printer control port to get the extra "bits"
you need.
Power wise using a transformer will probably be fine. The power line
frequency is not used for anything in the TV or VCR except possibly the
clock on the VCR which will run slow or fast.
Standards differ and you won't be able to watch or record broadcasts/cable
unless your equipment supports multiple standards.
to justify the added expense.
The technology of video recording makes interesting reading and the
sophistication of the circuitry and mechanism of a $200 VCR is quite amazing.
TVs are more likely to accommodate difference standards than VCRs.
Even a regular TV may be able to be used to play from a different
standards VCR. For example, NTSC 30/525 and PAL 25/625 use very similar
horizontal frequencies but different vertical rates and color encoding.
Playback will be possible (in B/W at least) if the vertical lock circuitry
(or the vertical hold control if there is one) on the TV has enough range.
A simple color code converter can then be easily constructed using a
couple of chips and some discrete parts.
However, some designs require a video input to stabilize the drum speed
and possible degradation (e.g., wow and flutter, noise, etc.) of the
recorded audio. Some VCRs will work fine without any video. Others
need it to stabilize the drum speed from the vertical sync. For best
results of audio-only recording, find a source of video-black such as a
camcorder with the lens cap on to minimize possible video interference
(though this is usually not a problem).
I don't think any stereo modulators exist, other than very expensive
professional models. The processing for TV stereo sound is much more complex
than FM stereo, involving dbx companding/NR on the L-R difference signal.
Hi-Fi VCRs mix the two audio channels together before feeding a mono-audio
modulator.
I laugh at all the people who buy a Stereo TV, HiFi Stereo VCR, then insist on
using the Channel 3/4 VCR RF outputs instead of the direct A/V connections.
They are getting MONO Sound!
You cannot do this without disabling the erase head(s). If this is done,
you will get interference from the previously recorded video - the rainbow
patterns present at the beginning of recordings over old material on VCRs
without flying erase heads.
Even if it were possible, I don't know how robust writing over the HiFi audio
tracks would be - you might get degradation after 1 or 2 dubs.
A UPS might be a solution but there are some issues to keep in mind:
If your VCR recently developed this amnesia, then you might consider
attempting to locate the cause (a shorted NiCd backup battery or bad supercap)
and correcting it rather than tying up a UPS for this purpose.
With the cost of reliable tape and disk storage units having enough
capacity to backup a 1 GB hard drive available or on the way for less
than $200, it doesn't make sense to use a VCR with a totally incompatible
format and questionable reliability when you will need it most - in a
data emergency.
I have no idea if the following is any good - I kind of doubt it - but
various products of this type were developed before devices like cartridge
tape (and now the Zip(tm) drive) backup became popular.
(From: Robin Gilham (gilham@stb.dfs.co.za).)
I saw an ad for a plug in card and software only yesterday, claiming
2G of storage on a 240 minute VHS tape. Wait.... yes, here it is.
The product is called "BACKER", and in .nl available from Timtronics
(+31-50-314 0937). Comes with interface card and Windoze software, will
backup harddisks at speeds of up to 9MB per minute for DFL159
(which is less than US$100).
(From: then@superpallo.cs.hut.fi (Tomi Holger Engdahl).)
The manufacturer of BACKER is Danmere Technologies Ltd and they have
WWW-pages at http://www.danmere.com/. What they claim by 9 MB per
minute, that is the data rate at the maximum speed, maximum compression
and minimum error correction. The uncompressed data rate is 5 MB
per minute at highest speed.
(From: Karl-Henrik Ryden (kalle@pobox.com).)
I have one of their cards. It works, but is rather tedious to use. It is
kind of like in the old ZXSpectrum/VIC64 days. :-)
OK, so you really want to just use its timer. There are two things you
would have to do:
Some (rare) VCRs have a switched outlet in which case this is trivial.
If removed from the VCR, you will need the complete specs on the digital
interface between the VCR's system controller and the tuner (assuming it isn't
on of those old types selected by mechanical switches!), as well a substitute
power supply. This information may not be available even if you purchase the
complete service manual. However, you may be able to infer it by monitoring
the relevant signals with an oscilloscope or logic analyzer :-).
An easier approach may be to use the entire VCR intact and interface via
the front panel (by simulating the Chan +/-, TV/VCR, etc. buttons) or via IR
by simulating its remote control.
The object in question may look like a pentagonal shaped frosted glass
slab with two pairs of wires sticking out of adjacent edges. What it is,
is an acoustic delay line implementing a one TV line (1H) delay - around 63
microseconds (NTSC). The crystal is a shaped cavity and the polished edges
are acoustic reflectors. There are a pair of piezoelectric transducers -
one to launch a wave and the other to pick it up. The acoustic waves bounce
around in a zig-zag pattern which increases the effective path length, thus
the unusual shape.
Uses in a VCR include a comb filter and tape dropout masking.
The comb filter is part of the chroma circuitry and computes the sum of
the current and previous video lines during recording and playback.
The acoustic delay line therefore implements a delay of exactly one
horizontal line. Due to the various games that are played with chroma
signal phase in the NTSC-VHS system (as well as Beta and PAL), the end
result is that chroma signal amplitude is doubled and crosstalk between
adjacent tracks is canceled out. This is because the chroma signal is
always exactly in phase between successive video lines but the crosstalk
between adjacent tracks is always exactly out of phase. The name 'comb
filter' is derived from the shape of the frequency response of the comb
filter - its evenly spaced spikes look somewhat like a hair comb and
it is used to 'come out' the crosstalk components of the chroma signal.
Another use for am acoustic delay line is dropout masking. The surface of
the tape is not always perfect - bits of oxide fall off or slight dips or
bumps result in momentary loss of head-tape contact. One way to minimize
visible streaks in the video is to replace the lost signal with video
from the previous scan line.
Nothing alien about it, just not your everyday electronic part.
There is no need for a comb filter in a camcorder!
Signals from the CCD are not first combined into CVBS to then be
separated by a comb filter again. That would make no sense.
(However, since modern camcorders are full function VCRs without a tuner, this
function may still be needed for dealing with external video input. --- sam)
Other applications for delay lines are drop-out compensation and delay
equalization between luminance and chrominance.
Did you ever wonder what happened to the ultrasonic glass delay lines that
were once used by the millions in every PAL television, for U/V separation?
They were replaced in nearly *all* applications by the Philips switched
capacitor delay lines TDA4660(-61,-62).
(From: David Lawson (dlawson@ime.net).)
the color signal(chroma) takes longer to process than does the b/w or
luminance channel so to get the color to line up with the b/w picture, the
B/W signal has to be delayed slightly.
They are similar - perhaps identical in some cases as the terms both
mean the same thing. If there is no optical output/input, then they
are likely the same type of device.
Optoisolators are used the switching power supplies to couple the feedback
from the low voltage to the line-connected (non-isolated) input.
With 4 leads, these are a combination of a an LED and photodiode or
phototransistor.
With 6 leads, there may be additional circuitry providing a logic level
output, or base connection to the phototransistor, or just extra unused pins.
Photo interrupters or reflective sensors are used for detecting reel rotation
cassette presence, and mechanism position. In this case the optical path -
either direct or reflective - is external to the device.
A datasheet will clarify any functional or circuit details.
Photo interrupters or reflective sensors are used for detecting reel rotation
Testing is accomplished (1) with a multimeter for shorts or opens on the
LED and (2) by providing drive to the LED and checking the resistance of
the photodiode or phototransistor with a multimeter - it should go down
dramatically if the LED is on.
Also see the sections on sensors and sensor testing.
Why are there so many totally different designs to do basically the
same thing? I fully understand the pressures of cost and manufacturability.
However, it would seem that with VCRs, for example, every manufacturer (of
which there are only a limited number who actually manufacture the
tape decks themselves) and every couple model years has a totally unique
design. You would think that after almost 20 years of manufacturing VHS
decks, the technology would be mature. True, there have been advances
with respect to quick start, HiFi, and so forth. Nonetheless, the required
functions have not changed. And, for that matter, the performance of the
typical mechanical deck has not improved that much in the last 10 years or
so. If anything, the old designs seem to be remarkably robust. I can
keep a 10 year old machine going virtually forever by replacing the rubber
every few years. I am not sure that I can say the same of a modern VCR.
Is it only a matter of maximizing performance at a given cost or is there
something more? NIH syndrome? Maintaining control over repair parts
and service? Or, use of entry level engineers who might provide a new
outlook on the design?
The repair place is jerking you around. It should not take them as long as
you have experienced to make a diagnosis - especially if they are authorized
and have the service manual. They like the really easy problems like
"My VCR started eating tapes last week. Is it hopeless?" 50 cents worth of
rubber (idler tire), charge $50 - easy money. And they appear to be heros.
To fix the electronic problems you need at least the intelligence of a carrot
and time - and time is money. OK, so maybe they give a quick cleaning also.
If it were my VCR, I would bitch, moan, claim poverty, threaten to report
them, etc. But, get it back and fix it myself. I assume you checked
the fuses. $80 dollars to fix doesn't sound like it could have been
much more than a fuse. With the typical markup on parts (4:1 for small
parts), those alone could easily push the bill to more than $80. The
longer they hold it, the tougher the problem seems so that when presented
with the (larger) bill the customer figures it is justified.
If this were a Sony, I would say that it needed a single drop of oil on
the half-loading arm shaft - which causes quite similar symptoms. Possibly
the JVC transport is similar.
At this point, there is not much wrong with the VCR - maybe a mechanical
problem like a stripped gear or the aforementioned gummed up lubrication.
It could conceivably be electrical like a dirty or worn mode switch.
However, I would go with something mechanical - and simple to identify
and repair.
Of course the latter is not a testimonial. Electronics chains make their
money from selling new VCRs not from repairing old ones. Therefore, they
may have incentives to discourage people from repairing their equipment
(though mucking it up is not the usual approach - simply declare it not
worth fixing - which is I guess what they did in the end).
They should have been able to clean the mode switch as a temporary fix
and confirmation of the problem. A broken gear would be obvious - they
should still be able to produce it for you - not that this would mean very
much as there is no way of demonstrating that it originated in your VCR.
Two months is way too long to wait for common service parts.
At this point, the timing is probably messed up - the novice bozo who was
assigned to your VCR had not read this document and violated Rule #1: always
mark all positions of mechanical components or adjustments before replacing,
removing, moving, or changing anything.
If the microcontroller is messed up, it very likely a result of what they
did. Their 'repairs' should not have made the situation worse. It used
to be possible to play a tape by helping the loading mechanism to complete
its cycle.
A reputable place would give you a total refund, no questions asked. Even
if it was your VCR that was hopelessly screwed up from the beginning, it
was their responsibility to recognize this.
Balderdash. The original symptoms simply do not support this in any way,
shape, or form.
This is much more likely. However, there still may be nothing seriously
wrong - the gears may just need to be retimed. This may require s service
manual, some consultation with a genuine JVC technician, or even another
similar model VCR tape transport to compare it with.
While anything is possible, I think, to put it bluntly, they do not have
a clue. Motors do not damage microcontrollers. There was nothing seriously
wrong when you took it to them - it should at least be possible to put it
back in that condition. Since they did not do this, whatever they did is
now the cause of more significant problems. However, it is quite possible
that even these can easily be remedied by proper timing of the gears and
mode switch - in addition, possibly, to that single drop of oil.
My recommendation would be to take it to an authorized JVC repair center
with this story printed out (not to blame the other people but to give them
something to start with). A competent technician should be able to quickly
determine what is going on. If they concur with your assessment of the
situation, then you can try to get your $30 back from the VCR repair shop
from Hell you have not already been credited.
For in-circuit tests with power applied:
Component values are not critical. Purchase photodiode sensitive to near
IR - 750-900 um or salvage from optocoupler or photosensor. Dead computer
mice, not the furry kind, usually contain IR sensitive photodiodes. For
convenience, use a 9V battery for power. Even a weak one will work fine.
Construct so that LED does not illuminate the photodiode!
The detected signal may be monitored across the transistor with an
oscilloscope.
Another (possibly better) view is shown in: VHS Tape
Format.
Note: ==== denotes the .15 mm guard bands between video, and the audio and
control tracks. Thus, once the audio, control, and guard bands are taken
into consideration, only about 10.65 mm or .42 inches is available for the
diagonal video tracks.
For a VCR with HiFi audio, the HiFi audio heads travel the same path as the
video heads but record their information just before the video heads pass
over the same spot on the tape. Although some of this is then partially erased
by the video, enough remains deep in the tape oxide to to permit reconstruction
of CD quality sound. The difference in azimuth angles of the video (+/- 6
degrees) and HiFi audio heads (+/- 30 degrees) minimizes interaction. (The
audio is also recorded on the linear audio tracks for compatibility with
non-HiFi VCRs.)
For a VCR with monophonic audio, the left and right audio tracks and their
guard band are combined into a single audio track of about 1 mm width.
Dimensions are most definitely *not* drawn to scale. The Audio and control
tracks are very narrow in comparison to the tape width. To get an idea of the
actual slant angle of the video tracks, imagine the tape stretched horizontally
by about a factor of about 10. (The length of a video track representing one
field or 262.5 scan lines is about 3.8 inches.) There are also actually more
than a hundred tracks at any given location side-by-side across the less than
0.42" available for the video information. This number of tracks is equal to
175 at SP, 350 at LP, and 525 at EP speed (for NTSC 525/60 - note that this is
not a coincidence but that is another story). Think of the alignment precision
needed for proper tracking! You can estimate this number by just timing how
long it takes for the rainbow pattern to wipe down the screen when re-recording
over an old tape at either speed on a VCR without flying erase heads and
multiplying this time by 60.
This book includes basic aspects of helical scan video recording; various
formats including VHS, Beta, U-matic, and 8mm; as well as advanced principles
of video encoding (with equations) relating to the chrominance and luminance
recording and playback channels.
I have found out that VCRs are produced by many manufacturers but if one
reads the "Sams' Photo facts" and checks the pin configuration on the LSI,
they will notice that there is a leg marked NTSC/PAL with either a low voltage
sign over the PAL or the NTSC symbol. In other words they manufacture 1 VCR
for both Europe and the US but either put a +5 V. or a Ground (Hi or Low)
voltage on the appropriate leg to make it either an NTSC or PAL VCR.
This is obviously to save money and manufacture 1 design for both the US and
Europe, but to change the voltage input based on weather that VCR is going to
the US or Europe.
I know this because, I shall relate the following story.
Aside from this inconspicuous notation in the Sam's Photofacts library which
I have access to, a person came to our shop from Colombia S.A. a few months
ago and said he would like his VCR converted back to NTSC !!!.
We told him, "What did you mean"? "It is impossible, these are made either,
or but not convertible". He told us that for $27.00 US he had his VCR
converted to PAL from NTSC. We opened the VCR to examine it and sure enough
there was a small 1" circuit board with a few wires coming from it and going
to the main board or mother board of the VCR.
We checked the Sams Photofacts and found hat the board was wired to a leg of
the CPU that had the notation NTSC/PAL !!!
It was then that it dawned on us that many manufacturers make 1 VCR with
Chips that have a leg that can be *TRIGGERED* to either generate an NTSC or
PAL signal.
I would like to get some of those little 1 inch boards that they use in South
America to convert or Trigger the CPU chips to generate a PAL signal in an
NTSC VCR. SONY US, HITACHI US and PANASONIC US deny any knowledge of this
but their technical manuals on their VCRs tell a *Different Story*.
Why is it that TV techs in a Banana Republic like Colombia know about the
conversion, but the Technical advisors at the corporate service centers in
the USA don't know about these "Special Modifications"?
If anyone has any information or experience in how to trigger the chips or if
they know where to get the little boards, that modify the vcrs. or how to wire
the VCRS so that they can be switched from NTSC to PAL, Please contact me.
It is characteristic of a house fire to generate 'fire debris', often
referred to as 'soot'. Fire debris, thanks to the plastic content of
a house and it's furnishings, is an airborne particulate, as small as
1 micron (um, 1/100th the diameter of an 'average' human hair) that
has a high petroleum content.
Internal air currents created by a house fire are often high enough that the
minutely sized particulate fire debris will find its way into the interior of
most consumer electronic equipment. Cabinets, covers, jackets, and the like
(unless they are totally airtight), are ineffective in preventing such
infiltration.
Fire debris is abrasive. While little or no damage is done to the
video tape that is wound tight on the reel(s), the exposed tape could
be contaminated, effectively making it as rough as a piece of fine
sandpaper. Cleaning videotapes after a fire prevents damage to the
video heads when the tape is later played.
(From: National Service Manager.)
Yes, with a model of that era, you have to twiddle each one individually.
Think of it this way: There are 16 or so memory locations each of which can
store the tuning info for one channel. You select the memory location, tune
your favorite channel in, set its real channel number, and the store that in
the memory location. So, when you are selecting channels with the up/down
buttons, you are actually indexing into a memory containing both the varactor
voltage and your channel number.
The easiest way I have found is to have a TV with its own tuner sitting next
to the VCR so you know which channels are which. If you do that, it really
doesn't take long.
The details will vary by model but it usually isn't difficult to figure out
the procedure with a bit of trial and error.
We have an huge, old, utterly-inoperative Fisher-Sanyo top-loader VCR that
we have kept for many years for the cat to sleep upon. I think the power
supply and the eternally-flashing display probably put out about ten
watts.
Sebastian the Cat (black-and-white male, long-haired, with the demeanor of
a Supreme Court Justice) started the practice when the VCR was a working
affair and I'd watch my Mississippi State U. electric power course tapes on
it. We brought it with us when we moved to Athens. When the VCR
developed sufficiently severe mechanical problems to warrant its
replacement we kept it for the cats. On Sebastian's passing, it was
inherited by Samantha, the small calico with impeccable white paws and a
large attitude. The VCR is now inhabited exclusively by Marmalade, the
long-haired orange tabby Mississippi beauty queen who was adopted from a
Starkville parking lot.
She's over there right now, asleep upon its silver plastic expanse, curled up
with her nose buried in her fluffy tail. It's always 0:00 pm for a cat.
(From: Jim Stanisich (jstanisi@isd.net).)
I can tell you about the Gemini. The voltage required is 18 VDC at 300 mA. The
three frequency. settings are set at the factory in the 900 Mhz band. You can
change these if you wish by removing the cover, and you will see three
corresponding trimpots near the front of the transmitter. They can be set
anywhere from 900 to 940 Mhz with a frequency. counter. Also by the antenna
there is a tin enclosure which is the RF amp. Inside there is a B+ pot
and a trimcap. These can be adjusted to produce a output of approx. 7 mW
instead of 1 mW. If you turn it up too high the video will distort so
watch the received video if you do this to keep it linear.
Note that the access holes in the RF section are covered with solder from
the factory. Sometimes they did such a good job you don't even know they are
there.
If you are tackling an electronic fault, a service manual with schematics
will prove essential. Some manufacturers will happily supply this for
a modest cost - $20-50 typical. However, some manufacturers are not
providing schematics - only mechanical and alignment info. Confirm
that a schematic (not just a block diagram) is included before purchasing
if possible.
Sams Technical Publishing (formerly Howard Sams) publishes Sams Photofacts
service data for almost every model TV that has ever been sold but their
selection of VCRfacts is limited and the newer ones tend to have strictly
mechanical information. However, they are worth a shot, especially if your
local large public library subscribes to the Sams series as many do. Some of
the older VCRfacts are quite detailed and complete.
In addition to Tandy products, there is at least one Sony model. Furthermore,
since Tandy does not manufacture its own VCRs or camcorders - they are other
brands with Realistic, Optimus, or other Radio Shack logos - your model may
actually be covered. It may just take a little searching to find it.
For camcorders specifically:
Not much there now but they do have some photos showing the disassembly of
a Sony camcorder which might be of use to someone.
If you want to get an idea of what is out there, search for the keywords 'VCR'
and 'repair' at http://www.amazon.com/. Several dozen titles are listed.
(I have no affiliation with amazon.com nor am I suggesting that you purchase
from them, but the search engine is convenient.)
Here are a couple of typical titles which I have used (there are many others
and I am not necessarily recommending these above the others):
From the advertising blurb for this book:
"PROMPT Publications, an imprint of Howard W. Sams & Company, has
released the In-Home VCR Mechanical Repair and Cleaning Guide, a
comprehensive guide that anyone can use to fix their own VCRs at home
(even start a VCR repair business). Full of illustrations, diagrams,
and helpful, step-by-step instructions. ISBN #0-7906-1076-0. $19.95.
222 pages. Call 800-428-7267 to order or for more info."
(From: Neil Preston (npreston@cctr.umkc.edu, npreston@CCTR.UMKC.EDU))
If you teach consumer electronics repair, I've run across a text that you
should check out:
I've looked at several VCR repair books in the past, and almost all of them
are very weak on the explanation of the mechanical problems in VCRs, which
account for 90% of the problems. This text does an excellent job of
explaining exactly how the tape transport system works in VCRs and what each
part does. It has lots of photos with parts clearly identified. It assumes
NO prior experience. I believe I could take a beginner student and let him
walk his way through it.
The table of contents pretty well describes it:
This is by far the best book I've seen on the subject.
(Please note: I have no connection with the publisher nor anything to gain by
bringing this to your attention.)
For basic mechanical problems, I could not have said the following any better.
One of the best I have seen is called:
This book describes in a step-by-step fashion how to repair a VCR without
expensive test equipment or special tools. Fixes are described for
different machines by brand & model #, and there is also a list of parts
suppliers.
I'm not affiliated with these people in any way - just impressed with the
book.
Here are a few mnore:
This one is even more basic but does cover the most common problems and has
illustrated instructions for video hookup, cleaning, rubber parts, cassette
repair, etc.
(From: cx163@FreeNet.Carleton.CA (Morton Lee Cohen))
Some of the books that you can find in your local library about the repair of
VCRS are listed below. One of the good books is HOME VCR Repair Illustrated.
These are all in the EE section: 621.38.
How do you determine the actual manufacturer? For most types of consumer
electronic equipment, there is something called an 'FCC ID' or 'FCC number'.
Any type of equipment that may produce RF interference or be affected by
this is required to be registered with the FCC. This number can be used
to identify the actual manufacturer of the equipment.
A cross reference and other links can be found at:
The chart below probably has your VCR so you probably do not need to
use the Web resource.
(From: William Miller, ASEET, eagle@trader.com)
This is a chart used to find the original manufacturer of a VCR. Find the
FCC-Listed or UL-Listed code (first few digits), then you'll see who REALLY
made it!
(1) Matsushita is the parent company of Panasonic, Quasar, and Technics
(2) (North American) Philips is the parent company of Magnavox and Philco
Sears model series to original manufacturer:
Assuming you cannot locate an actual part number, determine the type of
belt; square, flat, or round. If you do not have the old belt, this is
usually obvious from the pulleys. Most small belts (as opposed to V-belts
on 1 HP shop motors!) used in consumer electronic equipment are of square
cross section though flat types are sometimes found in the main drives of
VCRs, cassette/tape decks, and turntables (remember those?). Measure or
estimate the thickness.
The IC is always specified with the belt fully relaxed. This can be
measured by hooking the old belt on one end of a ruler and pulling it
just tight enough so that it more or less flattens out. Read off the
length, then double it for the IC. Get a new belt that is 5% or so smaller
to account for the old one be somewhat stretched out. Of course, if the
belt broke, measurement is real easy. Or, if you do not care about
the old belt, just cut it and measure the total length.
If the old belt decomposed into a slimy glob of jellatinous black goop or is
missing, you will need to use a string or fine wire around the appropriate
pulleys to determine the IC. Reduce this by 10-25% for the replacement.
Very often the match does not need to be exact in either thickness or
length - particularly for long thin belts. A common rubber band may in
fact work just as well for something like a tape counter!
However, there are cases where an exact match is critical - some
VCRs and belt driven turntables or tape decks do require an exact
replacement for certain drive belts but this is rare.
Some parts suppliers make determining replacement belts very easy with
the PRB system in which the part number fully codes the shape, size,
and thickness.
Idler tires are specified by their inside diameter, outside diameter,
and thickness. Some parts catalogs provide actual size drawings so that
all you need to do is match up your old tire to the picture. Since
tires do not generally decompose or stretch significantly and hold their
shape, measurement is usually quite easy,
Pinch rollers are specified by diameter and height along with bearing
inside diameter. The match must be exact so using the original
manufacturer's part number is best but generic replacements are available.
Parts suppliers generally provide quite complete cross references to their
replacement rubber parts and complete belt kits are available for most
model VCRs.
The bottom line: Most of the time, this stuff serves no essential purpose
anyhow and should be removed. A non-corrosive RTV or hot-melt glue can be
used in its place if structural support is needed.
One comment: make sure you scrape and clean off all the old glue. I have
heard and seen cases where this stuff turns conductive with obvious bad
consequences.
Note: do not mistake the hot melt glue or silicone sealer often used to anchor
capacitors or other large components to the circuit board for leakage. One
tip-off is that leaking chemicals will not tend to climb up the side of a
component! However, if it is on the circuit board and decomposed, various
erratic symptoms or other failures are possible.
(From: Gillraker (eternity@mail.cybertron.com).)
Extremely common in older Mitsubishi's!!!! Take it off of all your circuit
boards, some of that old glue is caustic, it eats into the traces and becomes
conductive as previously mentioned...sure way to tell is look at it and see if
it is rust colored around the edges....and there doesn't have to be much rust
either...that glue still puzzles me at times....even had to replace leads that
have been eaten totally away....
(From: Alan Hurst (alan@sastro.demon.co.uk).)
I had a dead display on my Sony SLV-777 (similar to 715 and 747 models) which
turned out to be caused by a leaking capacitor in the power supply. The leakage
had eaten through two tracks which supply power to the display.
The problem with leaking capacitors on the PS secondary is apparently very
common to the extent there is a service kit available from Sony to replace all
the capacitors on the secondary side of the power supply and has caused a wide
range of strange faults in this range of models.
For example:
(From: Paul Weber (webpa@aol.com).)
There is a very good chance that there is no "variable resistor" for adjusting
the head switching point or anything else in your machine. Most recent Sonys
use are setup entirely with an EEPROM which is programmed with a special wired
remote control (RM-95). Even if there is, you are going to need the shop
manual, or you run a high chance of breaking something important just taking
the thing apart.
(From: Varlod (varlod@aol.com).)
I recently got a job where I will be doing repairs on VCR's. I have been
out of the business for a short while. I just got a service manual to
repair a Panasonic AG-131 and noticed a few changes. I remember servicing
JVC VCR's in the mid 80's and they had dozens of pots on each board. This
VCR has none!! The electronic adjustment section of the service manual
tells you to put the VCR in the service mode, put in an alignment tape and
let the VCR do all the adjustments. This is incredible, are most other
newer VCR's the same? Of course I still have to do the mechanical alignment
if needed, maybe in a few years that will adjust itself also.
For safety related items, the answer is generally NO - an exact replacement
part is needed to maintain the specifications within acceptable limits with
respect to line isolation, X-ray protection and to minimize fire hazards.
However, these components are not very common in a VCR except for the
power supply.
For other components, whether a not quite identical substitute will work
reliably or at all depends on many factors. Some deflection circuits are
so carefully matched to a specific horizontal output transistor that no
substitute will be reliable.
Here are some guidelines:
The following are usually custom parts and substitution of something from
your junk box is unlikely to be successful even for testing: SMPS (power
supply) transformers, interstage coils or transformers, microcontrollers,
other custom programmed chips, display modules, and entire power supplies
unless identical.
However, for consumer electronic equipment repairs, places like Digikey,
Allied, and Newark do not have the a variety of Japanese semiconductors
like ICs and transistors, or VCR specific components like RF modulators,
idler assemblies, belts, tires, pinch rollers, video heads, etc.
See the document: Major Service Parts Suppliers
for some companies that I have used in the past and others that have been
recommended.
For VCR parts in particular:
See the additional comments below about Studio Sound Service. (I have no
affiliation with this company but have purchased parts from them.)
Also see the documents: "Troubleshooting of Consumer Electronic Equipment" and
"Electronics Mail Order List" for additional parts sources.
If you work on VCRs occasionally, for yourself or friends, you know that
most VCR problems are mechanical in nature, and usually require a replacement
idler, belt kit, or other small mechanical part. Most of these parts are
inexpensive, but you run into a problem when you try to order from
electronics distributors -- most require a $20 or $25 minimum order.
Studio Sound (see the previous section for contact info)
stocks a large selection of VCR parts, including belts, idlers,
gears, mode switches, semiconductors, etc, and will ship direct to you
with no minimum order! Our prices are competitive with electronics
distributors such as MCM and others, but you can order as little as one
belt, and we'll ship it. Just the cost of the part, plus $5.00 shipping
is all you pay. Many distributors charge $6.00 or $6.50 shipping, in
addition to the $20 or $25 minimum order!
We'll even help you determine which part you need, if you don't have the
part number - at no extra charge.
Need a part for a VCR? Fax or Email the information to us, and we'll
respond with a price quote before you order. We accept check, money
order, Visa or MasterCard - sorry, no CODs. Send all of the information
you have (make, model, part description, part number if you have it), plus a
return e-mail address or fax number, and we will be glad to give you a quote
on your part. Don't wind up paying $25.00 plus shipping to get a $3.00 part!
Let us help.
We also stock a large selection of Panasonic switch mode power supply rebuild
kits, and have just added Samsung power supply rebuild kits to our line.
The following companies are sources for inexpensive used VCR parts:
Huge quantities of used and rebuilt VCR parts. A lower drum for a two-head
machine usually goes for around $15. Major parts come with a 30 day
warranty. Well, it beats no warranty, I guess!.)
These are even better than junk yards as they do the searching and pulling
for you. For major subassemblies in older VCRs, this may be the only realistic
economical option even if the original part is available from the manufacturer.
Look in the Thomson (a.k.a. RCA and GE) "VCR/Camcorder Sourcebook"
TCE publication # 1J9780 available from your local Thomson distributor.
Publish date October 1994 (maybe newer version is out now)
This book lists the most common parts for many brands and models of VCR
and tells which Thomson or SK parts fit. Also has some solid state parts
listed crossed to Thomson part #. RCA VR470 uses belt #192179 or SKBK0516
and pinch roller #202113. Similar to VR450 through VR475, made by Hitachi.
Service manuals for RCA/GE/Thomson are available from Thomson Consumer
Electronics publications, P.O. Box 1976 Indianapolis IN (317)-267-5799.
Or maybe their at 10003 Bunsen Way, Loisville, KY 40299.
Microfiche for VCR is about $10. Older model series are available by the
year for good prices. I bought 1985 to 1990 for $50 or so. I have the
microfiche for RCA VR470. Also looked through my file cabinet and found
a printed service manual for VR470 in excellent condition, only used once.
Have extra microfiche set for 1985 vcr including models VLT250 to VLT470,
VLT600HF to VLT700HF, VLP800 to VLP970HF. I'll sell those service manuals
for a good price maybe $15 or so? (will pay for shipping). Or I'll check
with local high school electronics class if they want them. Don't know if
they are still fixing vcr or not, last time I talked to instructor he said
it was too many problems and they were getting away from repair.
Tandy (Radio Shack) can order PRB belts and have a CDROM to look up model #
belt guide. For just one set of belts, Radio Shack is much more accessible
to people then mail order with $20 minimum orders and shipping/handling.
-- end V3.17a --
Tom's comments on approaches to cleaning
(From: Thomas L DeTogne (tdetogne@home.com).)
Lubrication of a VCR
The short recommendation is: Don't add any oil or grease unless you
are positively sure it is needed. Most parts in a VCR are lubricated
at the factory and do not need any further lubrication over their lifetime.
Too much lubrication is worse then too little. It is easy to add a drop
of oil but difficult and time consuming to restore a VCR that has taken a swim.
"I heard a horror story when I was in tech school about someone who heard a
little squeaking inside the VCR when it was in PLAY mode, so he sprayed WD40
in through the tape door (front loading) and 'lubricated' the entire inside
of the VCR. The students who were working on this took apart the entire
mechanism, sprayed it clean with TF solvent (4 cans - there goes the ozone)
and it still didn't work. No surprise."
Head demagnetizing
With audio tape decks, demagnetizing is often recommended to improve
sound quality and frequency response. There is some debate as to
how much benefit there is to this practice but if done properly,
there is little risk. Demagnetizing removes the residual magnetic
fields that can build up on ferrous parts of the tape heads and
various guideposts and other parts in the tape path which may affect
frequency response.
Homemade VCR head demagnetizer
Rather than trying to build something that plugs directly into the AC line,
use an *AC* wall adapter. Typically something from an old modem with a rating
of around 1 A at 12 VAC should be fine. There is no significant safety
hazard to touch connections with power on and they are short circuit
protected so no matter what you do, there will be no immediate damage
to the adapter.
Building a bulk tape eraser
A variety of approaches work for this - all based on strong magnetic fields.
These will erase floppy diskettes, audio and video tapes, and all your credit
cards and Turnpike passes!
Cassette and Tape Loading Problems
Cassette loading and eject problems
Cassette loading places the cassette into proper position on the tape
transport. In a front loader, pushing the cassette gently into the
slot should cause a motor to take over and suck it in and down to rest
on indexing pins. The mechanism that actually holds the cassette is called
the cassette basket. Several types of problems are possible: the VCR may
ignore you when you push the cassette in or press EJECT, or it may
spit it out immediately or cycle back and forth. On a top loader, you do
most of the cassette loading manually, so the only likely problem will be
if EJECT does not work.
Ejecting a cassette from an uncooperative VCR
It is a common experience - the rental movie is due back at the video
store **now** but no matter how you press the EJECT button, yell, scream,
hold your breath, or jump up and down, the cassette refuses to be appear.
VCR is confused - will not eject non-existent tape
If for some reason, the microcontroller gets confused and refuses to raise
the basket and there is no tape in the VCR, first, try pulling the plug
for a minute or two. This may reset the error condition. However, since
the mechanism is in an illegal state, the microcontroller may refuse to do
anything for fear of making things worse.
Fast Forward and Rewind Problems
VCR will not fast forward and/or rewind
Usually, the owner will admit that the machine is pre-Jurassic and
has never been cleaned or serviced.
VCR aborts fast forward or rewind
In this case, the tape starts to move - possibly at a reasonable speed -
but then may shut down - possibly erratic or tape dependent.
Noisy REW or FF
While these operations are never exactly quiet, when grinding or squeaking
noises are evident, it is time to at least consider the possibilities.
Tape rewinders
Should you buy a tape rewinder to save wear and tear on your VCR?
Take it or leave it. I think they are good if your VCR is old and
for whatever reason has trouble with FF or REW. However, sluggish
FF or REW may be a precursor to tape eating and should be addressed to
avoid an impending failure which may ruin a tape. Rubber parts deteriorate
by just existing. The surface layer oxidizes and use may actually
be good (don't quote me!).
Play and Record Mechanical Problems
Quick list of common mechanical problems
The following aren't in any serious order but those toward the top of the
list are the most likely to occur:
VCR refuses to record
If efforts to record (directly or via the timer) are totally ignored or
cause the cassette to be ejected, then the record protect tab on
the cassette may be broken off or the record protect sense switch in the
VCR may be dirty or defective. This switch sits just under the cassette
slot (on front loaders). Locate it by referencing the tab position on the
loaded cassette. It can easily be tested with an ohmmeter - if you can get
to it. To confirm, short out or disconnect (which you will need to do
depends on the design of your VCR) the appropriate wires (maybe
there is a connector - this could have bad contacts as well) and see if
the VCR is more cooperative.
VCR aborts play or record during startup or shortly thereafter
This is a problem with the process called 'tape loading' - pulling the
tape loop out of the cassette and wrapping it around the spinning video drum,
engaging the capstan and pinch roller and reel rotation.
VCR aborts play or record at random times or near end of tape
In this case, the VCR starts to play or record but, say, an hour later,
shuts down for no good reason - at least not as a result of a command
you thought you issued.
VCR eats tapes
The most common cause of a VCR eating tapes is a dirty/worn idler tire
preventing the takeup reel from turning. See section:
General guide to VCR cleaning and rubber parts
replacement. The idler tire transfers motor power to the appropriate
reel hub. If dirty, worn, dried out, glazed, cracked, or otherwise
deteriorated, it will slip and cause the takeup reel (in
play mode) to stop turning at some point. Hopefully, the microcomputer
senses this and tries to wind the tape back into the cassette. But,
you guessed it, this requires the idler tire so you end up with a mess
of tape inside the machine. When you go to eject, you may get the cassette
with a tape loop hanging out. If you are careful, you may be able to
extract the tape without crinkling it too badly but don't just pull - it
will break or be hopeless damaged. You will need to remove the top cover
and carefully lift the tape loop out of the machine and wind it back into
the cassette. If there is any significant crinkling or a partial break
in the tape, discard the cassette. If it is priceless and irreplaceable,
see the section: Recovering damaged or broken tapes.
DO NOT try to use it or just return it to the video store without informing
them of what happened - it is unfair the next renter as a badly crinkled or
partially broken tape can destroy expensive video heads.
Tape loop hanging from cassette when ejected after play or record
(This may also apply to other modes for a VCR with a 'quick start'
or 'instant start' transport.)
Tape slows or stops (as though in pause or slow mode) while playing
What this means is that the tape continues to show a picture but it appears
as it's struggling to pull the tape through the machine - which is basically
what's happening. Once the picture freezes, it will probably abort due to
the lack of reel motion.
Video head drum stops or slows during play or record
Check whether the backtension on the tape is applying so much
pressure to the drum that it is slowing it down. Backtension should be
just enough to keep the tape in good contact with the drum. If it is too
tight, then you backtension felt may be worn or adjusted too high. There
is a lever just as the tape exits the cassette - push this to the right to
reduce tension. Someone may have attempted to repair a broken backtension
band and reduced its length - I got a VCR for repair once where this was
done.
Tape sticks to head drum
(From: Gary Woods (gwoods@albany.net).)
General Control Problems
VCR is alive but will not do anything
Typical symptoms: front panel display is active, it may be possible to
set the clock or timer and change channels, but all transport related
buttons are totally inert. Perhaps there is no response to any button.
The VCR may or may not refuse to accept or eject a cassette.
VCR clock does not run
The clock runs either off the power line (zero crossings of the 50 or 60 Hz
waveform) or from a crystal (possibly a reference derived from one of the
other frequencies used elsewhere in the VCR). Conceivably, a bad backup
battery or supercap might result in the clock remaining in setup or power
fail mode.
VCR attempts to play non-existent cassette
You turn power on or just plug in the VCR to the AC outlet and it
goes through the whirring sounds of playing a cassette - but there
is not cassette present.
Erratic behavior in various modes
You press PLAY and the VCR gets halfway through loading the tape and suddenly
aborts and shuts down. Or, you put a cassette in and it is immediately spit
out as though it tasted bad to the VCR. Or, you press PLAY and the VCR goes
into REWIND mode. Or, you pressed REVIEW and it ejected or attempted to
eject the cassette.
VCR mode (sensor) switches
In order for the microcontroller in a VCR to confirm correct functioning and
completion of various operations like cassette and tape loading and roller
guide position, some mechanical sensor feedback is normally used. The most
important sensor assembly in most VCRs is called the 'Mode Switch' or 'Mode
Sensor'. The purpose of the Mode Switch is to inform the microcontroller
of the gross position of the mechanism at all times. For example, the mode
switch may have 5 positions:
Mechanical relationships in VCRs
The complexity of the mechanism in a VCR can be quite intimidating. To
avoid total frustration and really messing up your day, before you remove
anything mechanical, take careful notes of precise relationships of
any gear, lever, switch, anything that might possibly get back together
in an ambiguous way. Often there are 'timing' marks on the gears just as
you would find in a lawnmower or automobile engine. These will be little
arrows or holes which will line up with stationary marks or with each other
on adjacent gears when the mechanism is in a particular position. Often,
it is best to put the mechanism in the position where the timing marks
line up because there may be fewer levers, cams, etc. which are under
pressure or tension in this position and thus fewer things to pop out at
you. If there are no apparent timing marks, make your own with a scribe
or pen. Sometimes mechanisms that at first appear not to be critical are
obscured in such a way that they really control critical timing. So, when
in doubt, make more notes than necessary - with diagrams. In rare instances,
there may even be a diagram showing the timing relationships pasted to the
bottom cover or stamped on the chassis. What a concept!
Intermittent behavior
This may mean that pressing on a circuit board, flexing a cable, or operating
the VCR in different orientation affects behavior. Sometimes this is affected
by temperature as well.
VCR does not work after cassette was forcibly removed
You were watching your favorite tape and suddenly the VCR emits a
mechanical eek and is now dead - or you press eject and the VCR shuts
down without regurgitating your tape. Worse yet, someone (we will not
point fingers) forcibly removed the tape to return it to the video store.
If this is not enough for you to get the hint
Here is a true story of forced eviction of a tape and the consequences. :-(
This teaches you two lessons: Don't use violence to remove a stuck cassette
and mark all gear, lever, sliders, etc. timing relationships before you
disturb anything!
VCR is failing the power-up sequence
This often means that the internal microcomputer found the mechanism in
an unusual state and was unable to reset it. Some VCRs will actually
move portions of the mechanism to make sure that everything is OK
to accept a tape. Failure here may be the result of a slipping or broken
belt or a belt that has popped off of its pulleys, gummed up lubrication,
or some other mechanical fault. How old is it? Rubber parts tend to
become smooth and lose their elastic properties ('rubberiness') after
a few years. Does the VCR make any kind of whirring sounds before
shutting down? This would mean that it is attempting to move something
back into position. Is there a tape in the machine? How about a toy, peanut
butter and jelly sandwich, or a little applesauce? It could be a sensor
or other electronic problem, but check out the mechanical possibilities first.
VCR displays DEW warning
Your VCR has worked fine for several years but now you get the 'DEW'
warning in the display and no tape functions work.
VCR shows LOCKED in the display
You go and try to play a tape and the VCR displays the word 'LOCKED'
or perhaps just a flashing 'L' or 'PL' in the display.
VCRs with Alzheimer's Disease
Suppose your just-out-warranty VCR is now acting up for no apparent
reason - making strange sounds, forgetting its programming, refusing
to cooperate, etc.
VCR has gone whacko
You may think you are on the set of the latest sci-fi movie. The VCR
displays are counting at random, pushing buttons produce unexpected results,
motors may be spinning, or the VCR may be repeatedly loading and unloading
a non-existent tape. I may be attempting to play a tape even without
you pressing any buttons.
VCR forgets settings following power failure
Normally, the AC line provides power to retain the clock, active channels,
and programming settings. During a power failure, the clock and programming
is usually powered using a supercap or battery (usually rechargeable).
Channel settings for older style varactor type tuners were often stored in
some kind of non-volatile memory while active channels for quartz tuners
generally use battery backup.
Display is dim
Where the display works but is dim, there can be several causes:
Display is dead but everything else works
This usually means that one or more of the voltages to the vacuum fluorescent
display (VFD) are missing or that the display controller is bad. If the front
panel suffered physical damage, the display tube, circuit board, or other
components could be damaged.
Pin 1: Filament 1A Pin 2: Filament 1B (Tied together)
Pin 5: Grid 6 Pin 6: Grid 5 Pin 7: Grid 4 Pin 8: Grid 3,
Pin 9: Grid 2 Pin 10: Grid 1 Pin 11: Grid 0
Pin 12: Segment 8 Pin 34: Segment 7 Pin 35: Segment 6,
Pin 36: Segment 5 Pin 37: Segment 4 Pin 38: Segment 3,
Pin 39: Segment 2 Pin 40: Segment 1 Pin 41: Segment 0
Pin 44: Filament 2A Pin 45: Filament 2B (Tied together)
Play and Record Control Problems
VCR randomly switches speeds, tracking problems, and muddy sound
First, don't ignore the possibility that you are attempting to play an
old, worn, or defective tape. This is especially true of rental tapes
which have been through who knows what kind of VCR hell. The control
and audio tracks - along the edges of the tape - are the first to wear.
Weak muddy sound and erratic tracking are also common symptoms caused
by old worn tapes. There have even been instances of new name brand tapes
which were cut too wide - though this would be extremely rare.
"One thing that can happen is that the control track head gets a ridge on it
(due to wear) which prevents the tape making good contact with it. This can
make the tracking go mad and sometimes even mute the video. Pausing the VCR
overrides any muting, resulting in a clean still picture. Another clue is
that some tapes will do it worse than others, this is due to slight
variations in tape width or condition."
VCR plays but at fast forward speed (or beyond)
Normally, speed is controlled via phase locking the capstan to the 30 Hz
control pulses read off of the tape via the stationary audio/control head.
Tape edge gets creased and/or random switching between speeds
As always, rule out the possibility that this is just a bad tape. There have
even been instances of new name brand tapes which were cut too wide - though
this would be extremely rare. It could have been creased by someone else's
VCR. Try a tape you can afford to sacrifice (though it will still be safely
usable) and run it through the VCR. Sometimes, there will be a problem only
near one end so you will need to try it at various sections of tape. Record a
few minutes and then back it up a bit and inspect for damage by opening the
cassette door (press the release on the side). Both edges should be perfectly
flat and smooth. If you get similar playback symptoms with this cassette
and/or find that the tape is being creased along one or both edges, then it is
your VCR doing the dirty work.
Recording stops at random times on previously used tapes
Symptoms may be that the tape counter stops moving and/or the VCR
enters stop mode and shuts down. Assuming this is not a mechanical
problem - bad idler, belt, etc., make sure you don't accidentally
have an 'insert editing' mode enabled. Insert editing uses the
previously laid down control track as the timing reference. This
provides clean glitch-free transitions between scenes. Insert editing
will not work at all on a new or bulk erased tape. If you routinely
use your cassettes over and over, there will be varying amounts of
previously recorded material - with control tracks - on the tapes.
At some point your recording may start to use tape beyond the recorded
sections and - presto, no more control track. Poor VCR is confused
and aborts.
Record (or play) stops after 15 minutes (or 30 minutes, etc.)
Make sure you are using the proper record button. Most VCRs have a
OTR (One Time Record) or 'quick record' feature which starts just like normal
record stops after a multiple of (usually) 15 minutes depending on how
many times you press the button. The (normally) red button should be
used for unrestricted untimed recordings.
Tape counter is erratic
The result may be inconsistent positioning of the tape if you use the
counts to locate programs. It might also result in the VCR aborting
PLAY, REC, FF, REW, or search modes if it thinks that the counter is
not changing as expected - missing pulses or skipped counts.
Video Play and Record Problems
Video playback problems
If the VCR works in all respects when tuning broadcast or cable channels
but playing a tape results in no picture, a very snowy picture, or just
a blue screen, there may be problems with the video heads, the lower cylinder,
head preamps, or other video electronics. Testing most of these is beyond
the scope of this document and will require a service manual and test
equipment. However, you can do a decent job of determining if the video
heads are likely to be at fault.
Video record problems
If attempting to record results in unexpected behavior, there could be
a variety of causes depending on what you get for playback:
Problems with playback of self-made recordings
This someone unusual possibility deals with the case where a tape can't be
viewed properly using the same VCR on which it was recorded.
Snow on one or more speeds
Did the problem happen suddenly? Or develop over time? If suddenly, what
were you watching at the time? A (literally) dirty rental movie?
Video turns to snow some time after vide head cleaning
What this means is that you are watching your favorite movie and in the middle
of the most exciting scene, and your picture turns to snow or a blue screen.
You performed what you thought was a thorough cleaning and then it happened
again.
One or more lines at fixed locations in picture
This means that there is one or more horizontal lines during playback that are
at fixed locations on the screen. These could be the result of electronic
problems or marginal video heads but the possibility that should be explored
first is that of tape damage.
Jumpy picture in play
You have a VCR with known good heads that produces jumpy (vertically)
video in play that cannot be stabilized with the tracking control.
Perhaps you have attempted to adjust the mechanical tracking and maybe
some other stuff. Some questions:
Picture shakes or jumps or has snow in PAUSE/CUE/REV
Note that on a 2 head VCR, it is not possible to display a noise-free
picture on a tape recorded at the SP or LP speeds. Therefore, for rental
or pre-recorded tapes, what you are seeing may be normal. A 2 head machine
should execute these special effects perfectly fine with EP(SLP) recorded
tapes, however.
Video search blanks out or doesn't work on recordings made at certain speeds
This may be a 'feature' of your VCR. On some older models, the designers
in their infinite wisdom (or that of their marketing departments) decided
that no picture or no search capability at all was preferable to a picture
with serious noise bars or one which didn't sync properly. This was usually
before the days of 4 head VCRs which directly addressed at least some of
these issues.
VCR plays pre-recorded tapes but its own recordings are noisy or jumpy
Problems will be similar to the following:
"I have a General Electric VCR model VG4217 that's displaying the most
unusual problems. When I play back a pre-recorded tape from a video store
it plays fine. When I play back a tape recorded on the machine I get video
noise for 4 seconds then clear pix, then video noise for 4 seconds, then
clear pix and so on.
Incorrect frame alignment or bad video for part of frame
Symptoms like a picture which has a portion that is noisy or missing,
or where the picture is split between top and bottom with the vertical
blanking somewhere in between may indicate a problem with the PG sensor.
Rainbow pattern in recordings made over previously recorded tapes
Unless your VCR has a flying erase head - located along with the normal
video heads on the rotating drum - you will see a faint rainbow pattern near
the start when recording over a previously used tape. The reason is that there
is a separation of a few inches in the tape path between the video heads
and the full width erase head. When you start recording at an arbitrary
point, it takes several seconds (actual time depends on recording speed)
totally erased tape to make it to the video heads. You are seeing
an interference pattern between the old and new video signals. The pattern
will slowly wipe from top to bottom as the diagonal tracks of new video
intersect more and more of the erased tape.
Barber poling - bands of rainbow or color
Some rainbow patterns are normal for the first few seconds of recordings
made on previously recorded tapes on non-flying erase head VCRs. See the
section: Rainbow pattern in recordings made over
previously recorded tapes. However, alternating bands of rainbow or
color indicate a fault sometimesreferred to as 'barber poling'.
Flag waving - top portion of picture wiggling back and forth
You have just loaded a videotape sent to you from your long lost cousin and
you notice that the top of the picture is wiggling back and forth. This
may be a VCR backtension problem but it could be much simpler.
Why do newer VCRs seem to be worse with respect to flag waving?
(From: Jeroen H. Stessen (Jeroen.Stessen@philips.com).)
Audio Problems
Total lack of sound on playback from non-HiFi VCR
This assumes audio from the VCR's tuner is fine. If ALL audio is missing,
check your external connections (particularly if you use the RCA jacks),
try switching to the other channel (3/4) if you use the RF output, and adjust
the fine tuning (if any) on your TV.
Poor quality sound on non-HiFi VCR
There can be several non-electronic causes for poor quality sound on linear
audio playback:
Identifying source of one-channel (non-HiFi) low audio/hum/buzz
Perform the following 'screwdriver and short tests' to narrow down a
one-channel low audio problem:
Excessive flutter on VHS linear (non-HiFi) audio playback
While general quality of VHS linear audio is almost always mediocre, there
should not be excessive flutter - wavering in pitch. Certainly it should
not be noticeable for speech. How bad music sounds will depend on your
expectations as well. Here are some possible causes:
No (non-HiFi) sound on new recordings
Sound is fine on pre-recorded tapes or tapes recorded on this VCR prior
to the problem developing. New recordings have no sound whatsoever.
Audio not present through VCR
Tapes play fine but audio is missing to the TV and when making recordings
using the VCR's tuner.
Previous (non-HiFi) audio is not erased on new recordings
If the old audio track is unchanged - you get the new video but old
audio, check that any dubbing switches are set correctly - to enable audio.
Poor quality sound on HiFi VCR
The VCR may be switching between HiFi and linear audio at random (with
the HiFi light also flickering on and off or simply not selecting HiFi
audio at all. This may be happening with only one audio channel (usually
the right channel in this case).
Help for marginal HiFi heads
Also see the chapters: "Video Heads and Upper Cylinders" and "Tape Path
Alignment and Backtension Adjustment".
hum or buzz in HiFi audio
(From: Liam Keane (106350.3410@CompuServe.COM).)
Fluttering or noisy HiFi audio
Where a VCR has seen a lot of use, the video and HiFi audio heads are likely
to be worn. However, evidence of video problems may or may not proceed HiFi
audio degradation:
Squealing noise from VCR in certain modes
Unusual noises from inside the VCR may be an indication of a problem or just
a badly made cassette - try a different one.
High pitched whine from inside VCR
Your first thought is probably of an expensive repair to a motor bearing
or replacement lower cylinder. If there is a high pitched whine coming
from inside the VCR when in PLAY, REC, or other mode which spins the video
heads, you may simply have a dirty or improperly positioned antistatic brush.
Tapes play back in a foreign language
"Have recorded tapes with a Mitsubishi U52 that play back in English on
same, but play back in Spanish with some other VCR's. What's up?"
Signal and Interference Problems
VCR color problems
There are two typical situations:
RF signal problems
First determine whether there is a problem with broadcast or cable, playing
tapes, or both. If it is only broadcast or cable, then your source may be at
fault. If it is fine with the VCR off but noisy when using its tuner, the
problem could be in the tuner itself.
VCR will not tune broadcast or cable
Are you sure that the input signal is making to the VCR? Does the pass-
through connection work? Double check the connections. Connect the cable
you have on the ANTENNA IN of the VCR directly to the TV. Make sure it's
center pin is not bent over or broken off. Try a new cable. Is the tuning
mode switch (broadcast, CATV, etc.) set correctly on the VCR?
Interference patterns such as parallel or diagonal lines
This may be due to the proximity of the VCR to a TV or other component,
outside interference, or a fault in the VCR.
Proximity to other equipment
Depending on the combination of VCR and the TV (or other A/V equipment),
there may be situations where either the VCR will not operate normally.
For example, placing the VCR directly underneath the TV may result in
erratic behavior or noise or other patterns in the video (playback or
record as well). All this means is that there is some RF emission from
the TV that is getting into the logic or video circuitry of the VCR. While
shielding is possible in theory, the only easy solution is to rearranged
your setup to they aren't so close together. There is really no way to know
which models are subject to these problems or which configuration(s) of
equipment will be best without trying them.
Firing (static) lines in picture during playback
These may be described as static or short bright or dark lines in the picture.
They usually have a sharp start and may trail off or stop abruptly. They may
be occasional (once every few seconds) or frequent (multiple instances per
video frame). Also see the section: Are your video heads
really bad? for video head problems as large quantities of firing lines may
be due to dirty, worn, or defective video heads.
General System Problems
Multiple system problems
Most VCR problems will be limited to a specific subsystem - video, audio,
tuner, servo, control. When multiple seemingly unrelated problems occur
at the same time, suspect a power supply problem since multiple systems
may be fed from common power supply outputs.
Power supply problems - unit totally dead/major system problems in all modes
Power supply problems can range from intermittent behavior due to slightly
out of tolerance voltages, hum, or noise to a totally dead VCR. Multiple
system failures can result if one or more of the half dozen or so voltages
used within the VCR are incorrect or missing.
Fuses and IC protectors in VCRs
A variety of protective devices are used in VCRs.
VCR power supplies
Reread Safety info before tackling any power supply problem in a VCR!
Internal fuse blew during lightning storm (or elephant hit power pole)
Power surges or nearby lightning strikes can destroy electronic equipment.
However, most of the time, damage is minimal or at least easily repaired.
With a direct hit, you may not recognize what is left of it!
Use of surge suppressors and line filters
Should you always use a surge suppressor outlet strip or line circuit?
Sure, it shouldn't hurt. Just don't depend on these to provide protection
under all circumstances. Some are better than others and the marketing
blurb is at best of little help in making an informed selection. Product
literature - unless it is backed up by testing from a reputable lab - is
usually pretty useless and often confusing.
Miscellaneous Problems
VCR poops out after a couple of hours
What could be the cause of the video dying on a VCR after it is
playing for a couple of hour? Here are some questions:
VCR blows fuse once in a blue moon
These are the kinds of problems that put gray hairs on parts of your
body you didn't think could grow hair (hey, maybe that is good).
VCR was dropped
So your cat decided it was time to practice the long-jump and didn't
quite pick a stable destination. Your VCR is on the floor, Tabby
is in the basement, and what to do?
VCR or camcorder went to the beach (sand and/or surf)
Someone took your camcorder to the beach this summer and now it has sand
or perhaps salt inside. Or, that cup of tea on top of the VCR wasn't as
stable as you thought. Now, it behaves, well, strangely. Can this
possibly be fixed? Will it be worth the effort or expense?
Dead or missing remote controls or lost codes for universal remotes
See the document: Notes on the Troubleshooting and
Repair of IR Remote Controls for extensive information as well as
links to the web sites of manufacturers of universal remote controls -
these include setup info.
Recovering damaged or broken tapes
So you just pulled your favorite tape from the VCR and there are two tape ends
dangling from it. Or, perhaps, your VCR has just munched on that tape and a
section is now seriously crinkled. Maybe you haven't been following the
recommendations on preventive maintenance; maybe your VCR was just hungry. In
any case, what to do? The recording is, of course, irreplaceable.
Uncrinkling a crinkled tape
WARNING: Discarding a seriously crinkled tape is really the safest option
from the point of view of the health of your VCR. However, if you really
must view it, there are some relatively low risk options. The following only
applies if there is absolutely NO evidence of even partial breakage or
puncture of the tape's backing (it's OK if some of the oxide has flaked off):
Disassembling a VHS cassette
These instructions should enable you to get inside a cassette for the purpose
of reattaching a leader that pulled off of one of the reels or to enable you
to transfer its contents or a portion thereof to another shell or vice-versa.
Cassette rewinder problems
Cassette rewinders typically consist of a low voltage motor powered from
a built in transformer or wall adapter, a belt, a couple of reels, and some
means of stopping the motor and popping the lid when the tape is fully
rewound.
Why VCRs will not copy (Macrovision) copy protected tapes
"I've got one of the Damark ones and it does work for Macrovision
protection, depending on the input deck. My 10 year old Panasonic VHS
Hi-Fi (No MTS tuner, Dolby(tm) B linear stereo non-Hi-Fi audio too) works
fine as an input deck, while my new JVC Hi-Fi doesn't. Why some input
decks work and others don't is my question. Anyone know? Is there
added circuitry that the newer decks have to defeat the stabilizer boxes?"
VCR AGC and Macrovision copy protection
(From: Mark T. O'Bryan (obryan@gumby.cc.wmich.edu).)
Problems with closed caption decoding
"I've just started to use the closed caption feature of my TV and have a
problem with pre-recorded video tapes, and am wondering if it could be the
VCR. The problem is simple: about half the tapes I've watched displays the
CC information incorrectly (many missing characters and/or lines), or will
not display it at all. Sometimes I can improve the CC display by adjusting
the VCR tracking to the point where the picture starts to become fuzzy, but
for the most part it remains garbled and uncorrectable."
F-connector broken off rear of TV or VCR
Sometimes this just happens due to poor manufacturing and a slight tug.
However, usually, there has been some severe trauma - like the TV or VCR
falling off a shelf while still attached. When else would it fall off a
shelf? :-)
Whirring sounds from VCR when tape inserted
The most likely cause is that your VCR uses an "instant start" transport
and the sound is from the video head drum spinning. The drum starts spinning
as soon as a tape is inserted and until several minutes after the last tape
motion ceases (PLAY, REW, CUE, REV). It's possible that due to wear, this
sound may become louder over time but should never get to the point of
being annoying. If there's a high pitched whine, the problem could be
the "static brush" associated with the head drum. See the section:
High pitched whine from inside VCR. Control/power
supply faults can result in the head drum spinning when it's not supposed
to on non-instant start VCRs but there would almost certainly be other more
serious problems.
A Few Model Specific Problems
Dead clock in Hitachi manufactured VCR
The clock display is dark but other functions are normal.
JVC tracking problems and dropped parts
You have a JVC VCR, 1990 or so vintage and it upped and died on you.
Magnovox tracking problems and dropped parts
(From: Frank Fendley (frank.fendley@datacom.iglou.com).)
Panasonic error codes
I'm not sure for which models these are valid.
01 - Drum motor stopped
02 - Tape reel stopped
03 - Mech stopped during loading to drum
04 - Mech stopped during unloading from drum
05 - Capstan rotation fault
06 - Mech stopped during tape-in/eject
Quick tips for troubleshooting Matsushita/Panasonic SMPSs
This general approach applies to most switchmode power supplies found in
Matsushita manufactured VCRs (includes Panasonic, some Quasar, RCA). Symptoms
may be a totally dead VCR, unresponsive front panel/remote but working
display, poor or erratic play/record, and/or random shutdowns.
Multiple system problems with various RCA, GE, and Samsung VCRs
Symptoms include anything from erratic behavior to acting totally dead. There
are many models for which the info below applies.
"I am currently working on a GE VCR Model VG-4016 with the following
problem. When the tape is inserted it loads fine the head starts spinning
but it doesn't play because the capstan is not turning. If you push play a
second time it start to play but is in the X2 mode so its going to fast."
Samsung (and clone) power supply problems
(From: Gilbert (osmyn@together.net).)
Erratic behavior of Sharp VCRs
Two words: Mode Switch (at least with older models, see below). Whenever you
have problems that seem to come and go or go away temporarily with repeated
attempts to play or enter some other mode, the problem is very likely a dirty
(or worn) mode switch (may be called the 'mechanical state switch' by some.
Late model Sony VCR munches tape on eject
Symptoms are that upon eject, a loop of tape may be hanging out and possibly
held by an arm inside the deck. The cause is gummed up lubrication on the
pivot of that 'half loading arm' on the right side of the transport. It is
supposed to help pull the tape out of the cassette during loading and then
spring back when unloading. If the lubrication gets sticky, it does not
spring back and grabs onto the tape during eject. Remove the half loading
arm by unscrewing the locking nut. Count the revolutions of the nut as you
do this since it sets the height which is somewhat critical. Clean the
bearing and shaft and then lubricate it with a drop of light oil or a dab
of light grease.
Sony VCR error codes
(From: VCRMonthly (vcrmonthly@aol.com).)
Code Problem
-----------------------------------------------
00 Normal.
01 Abnormal Take-up reel rotation.
02 Abnormal Supply reel rotation.
03 Abnormal drum (head) rotation.
04 Abnormal forward cam motor rotation.
05 Abnormal reverse cam motor rotation.
06 Abnormal cassette loading.
07 Abnormal cassette unloading.
Error Code Block Problem
--------------------------------------------------------------
00 No error
01 - 09 Control motor
(encoder) Unable to detect the position
10 Mechanism Loading not completed
11 (deck) Unloading not completed
12 " No eject
13 " End sensor fault (take-up side)
14 " End sensor fault (source side)
15 " Dew detected
20 Drum Drum motor won't rotate
21 " Drum servo not locked
30 Capstan Capstan motor won't rotate
31 " Speed not locked
40 Reel Take-up reel FG not locked
41 " Source reel FG not locked
42 " Measure abnormally ended (whatever this means)
Code Problem
-------------------------------------------------------------------------
00 No fault
01 Take up reel not rotating
02 Supply reel not rotating
03 No drum rotation
04 Clockwise rotation of capstan motor incorrect
05 Anticlockwise rotation of capstan motor incorrect
06 Cassette loading incorrect
07 Cassette loading incorrect
Sony capstan motor (bearing) problems
A typical set of symptoms and questions:
"The capstan motor on my Sony VCR has lost the war and is in need of
replacement. Based on my Dejanews search on this topic, this is evidently
not an uncommon occurrence :(.
Symphonic/Funai brand vcr won't rewind or fast forward
(Portions of the following from: blatter@amiga.icu.net.ch ((Martin A. Blatter))
Additional Symphonic/Funai comments
(From: Tony Buffone (uproc@Aol.com).)
Zenith model VCRs with erratic tracking of rental tapes
"Has anybody had any experiences with a Zenith VR2422HF VCR having
auto-track problems with certain rental tapes? This is the second one
I've had in the shop where it will switch back and forth between sp
and SLP speeds. has anybody seen any mods or heard anything?"
Video Heads and Upper Cylinders
What is a Video head?
The flying video heads in a VCR or camcorder are the actual transducers which
scan the tape during REC and PLAY. The head drum or upper cylinder,
as it is often called, spins at 1800 RPM (for NTSC, actually 29.97 Hz)
with one complete rotation representing a video frame (525 lines in the
US consisting of 2 fields which are interlaced). The result of the spinning
head is to provide an effective head-tape speed of over 24 feet/second needed
to achieve the required video bandwidth.
Video head construction
The actual video head chips themselves are mounted just about flush with the
lower edge of the spinning assembly called the head drum or upper cylinder.
They are made of ferrite - an extremely hard but fragile material. In terms
of physical strength, its properties are similar to glass. The head actually
consists of the core, pole pieces, and gap filler molded as a single unit and
fired at high temperature along with the coil wound on the core after firing.
This 'chip' is then glued to a metal support which is screwed to the bottom of
the drum. A screw presses against this support from above and is used at the
factory for final head height adjustment on the drum.
Diagram of single video head
The diagram below shows a typical single video head as would be found on
a 2 head VCR. Two of these (with opposite gap azimuth angles) would be
mounted exactly 180 degrees apart on the upper cylinder. This is a view
as would be seen from the bottom of the upper cylinder:
____________________________
| |
| _______ |
Coil+ o---------------+ | |---o Coil-
+------------+ +-----------+
. +------------+ +-----------+ .
. +------------------/ | .
. | \ / | . Side of upper cylinder v
-----------\____________||____________/---------------------------------
-->||<-- Record/Play gap, width about 1 um
The same head viewed from the edge:
______________ _____________ Bottom of upper cylinder v
------ |_____________//_____________| ----------------------------
| |
------------------------------------
|<---------- 1/8" ---------->|
Diagram of double video head
The diagram below shows a typical double video head as would be found on a VCR
with more than 2 video heads if video heads are grouped together. The quite
visible space in between the two head chips should not be confused with the
actual microscopic record/play gaps in the pole pieces even though the total
width of the two head chips (1/8") is about the same. For a 4 head VCR, there
would be two such assemblies (with opposite gap azimuth angles for each head)
mounted 180 degrees apart on the upper cylinder.
Coil1+ o o Coil2+
___________________ | | ___________________
| || || |
| ______ || || ______ |
Coil1- o---| | +----+ +----+ | |---o Coil2-
+-----------+ +----+ +----+ +-----------+
. +-----------+ +----+ +----+ +-----------+ .
. | \---------+ +---------/ | . Side of upper
. | \ / | | \ / | . cylinder v
--------\____________||___/-----\___||____________/---------------------
-->||<-- -->||<-- R/P gaps, widths about 1 um
The same head viewed from the edge: Bottom of upper
______________ ____ ____ ______________ cylinder v
--- |_____________//____| |____\\_____________| ----------------
| |
---------------------------------------------------
|<------------------ 1/8" ----------------->|
Photo of a typical upper cylinder
Here is a photo of a typical 6 head upper cylinder from a JVC HiFi VCR. This
unit was damaged by the infamous "floating roller guides syndrome" and one of
the head chips is smashed.
Upper cylinder (video drum) diameter
For most regular VHS VCRs, someone in their infinite wisdom picked 2.45".
Yes, there are probably good reasons for this - a compromise between tape
track length, writing speed, and so forth. Or, maybe it was the size of
the engineer's nearest handy juice can lid. :-)
How do the signals go to/from the upper cylinder
The rotating upper cylinder and stationary cylinder form a transformer - the
space between them is very small and coupled the signals between the primary
and secondary ferrite cores. Each of the heads for R/P video, HiFi audio, and
flying erase, are electrically independent. The cores are arranged coaxially
which should get to be pretty tight for a 6 or more head VCR!
Are your video heads really bad?
No picture (total snow or a blue/black screen depending on model) or a snowy
picture in play modes and/or failure to produce a good recording may indicate
dirty or bad video heads. First, make sure that the VCR's tuner and RF
modulator are working by viewing a broadcast or cable channel. Next, refer to
the section: Video head cleaning technique and follow
the instructions carefully. If there is no change even after a couple of
cleanings, then your video heads may have problems. Of course, if your
inspection reveals any physical damage, you will need a new set of heads
(new upper cylinder).
More on evaluating video degradation
(From: Frank Fendley (frank.fendley@datacom.iglou.com).)
Effects of video head wear on HiFi audio
(Portions from: Peter (peter@puttonen.com).)
Need for video head cleaning
When should you clean a video head? Only when symptoms point to a problem
with the head. See the section: Are your video heads
really bad?. Periodic cleaning is not necessary and may cause excessive
wear if done with a head cleaning tape, especially the dry kind which may be
excessively abrasive. Frequent cleaning by hand, while not damaging, still
represents a slight risk since you never can tell when you might do something
you will regret!
Automatic head cleaners
I do not see any advantage in buying a VCR which claims to have automatic
video head cleaning. Healthy video heads are basically self cleaning in any
case. The automatic head cleaner is a foam roller that contacts the rotating
heads for a couple of seconds when the tape is loaded. In my opinion, this is
worse than useless as any crud collected by this foam may just be redeposited
on the heads during the next cleaning cycle. So, if your VCR has this
'feature' and you experience symptoms of dirty video heads after each tape,
remove the 'feature' and performance will improve :-).
Video head wear and instant start VCR tape transports
While it may seem that this design - where the tape remains in contact with
the video heads even during FF and REW is a bad idea, additional wear, if
any should be minimal and not worth worrying about.
How NOT to clean your video heads or a very expensive lesson
The following is a true story. Don't let it happen to your VCR!
"Thanks a lot for the FAQ on VCR repair (unfortunately too late --- sam).
I now realize that I have made a boo-boo of quite unprecedented magnitude!!
You're not going to believe this... (I'm almost too ashamed to admit to
this!).
Video head cleaning technique
CAUTION: Read the following in its entirely to avoid an expensive lesson.
"A good quality automobile chamois (the real thing, not the fake
stuff), cut up into 1 to 2" squares, is far cheaper and easier to
manipulate than the sticks. After cleaning the heads, the chamois square
can be re-moistened with cleaning fluid and used to clean the A/C head,
rollers, guides, etc.
Rob's alternative video head cleaning techniques - use with care
(From: Rob-L (rob-l@superlink.net).)
Expected life of video heads
(From: Jerry Greenberg (jerryg50@hotmail.com).)
Advanced video head testing techniques
Assuming cleaning does not help and you have the time and inclination, some
additional test can be performed to confirm or rule out a bad set of video
heads (upper cylinder).
Measuring video head wear
You mean your thumb isn't calibrated to the micrometer (um)?
"I'm trying my hand at VCR repair. Sony specifies a hand-held device that
connects to a non-rotating video head and that measures how worn the head
is (Beta machine). I'm trying to imagine how it works. Is it the head gap
itself that gets bigger as the head wears?
More than you even wanted to know about video head tip penetration
Remember how I told you never to even think about adjusting the video head
chips themselves? Well, it seems some people never listen :-).
Highlight tearing and bad video heads
Highlight tearing - trailing lines adjacent to bright areas of the picture -
often indicates a worn video head. Sometimes, this only shows up severely
for tapes recorded AND played back on the same machine. Why?
Where to obtain replacement video heads
Once you have concluded that a replacement head is required, you need to
decide whether you will undertake this yourself or take the VCR to a shop.
Video head replacement is relatively straightforward and low risk as long
as you are comfortable working on mechanical devices and take your time.
A little unsoldering and soldering is usually required.
Upper cylinder not replaceable as a separate assembly?
On some newer VCRs, it seems that in the manufacturer's infinite wisdom (or
cost crunching), the normal video head drum or upper cylinder cannot be
replaced by itself. Only the entire expensive cylinder unit is available.
Video head replacement technique
How about when the head drum refuses to budge?
(From: Raymond Carlsen (rrcc@u.washington.edu).)
What if the replacement upper cylinder doesn't work?
There are a number of possibilities and one of the more common particularly
with generic replacements is, guess what? A defective replacement!
HiFi/video tracking problems after upper cylinder replacement
Unless you had such symptoms originally where best settings of the tracking
control for the HiFi audio and video are at grossly different positions, the
problem is with the video head drum itself or its installation.
Comments on HiFi tape path alignment
(From: Jerry Greenberg (jerryg50@hotmail.com).)
Tape interchangeability
Since video heads are not all manufactured exactly the same, there is a slight
chance that you will experience problems of playing tapes recorded on other
VCRs in yours. However, before adjusting the roller guides or other settings,
make sure that the *other* VCR is aligned properly.
What are the symptoms of a video head that is on backwards?
Suppose I screwed up and installed a video head 180 degrees rotated from
what is correct. What will happen?
Can I substitute a video head from another VCR?
The quick (and long) answer is: NO. The heads themselves are in
no way standardized. You can substitute a video head drum (upper cylinder)
if it is identical - VCRs sold under different labels are often manufactured
by the same few companies. Check a cross reference if you have a dead VCR
with a good set of heads but not the same model as the one you are
trying to repair. As far as the heads themselves, don't even think
about attempting to interchange the actual head chips - even if
your replacement were physically and electrically compatible, you would never
be able to get the alignment within tolerance since you do not have the
factory jigs. Not to mention that the head chips themselves are really
really tiny and really really fragile and their specifications
all vary - head width, azimuth angle, etc. Forget it.
Disassembling the lower cylinder
It is rarely necessary to do this but if you should - from curiosity or
anything else - beware that the reference for the #1 head may be a magnet
attached to the motor shaft. This may not be keyed and unless you carefully
mark everything beforehand, will have no way other than trial and error to
get if back at the proper angle.
Tape Path Alignment and Backtension Adjustment
General tape path alignment procedures
There are separate descriptions of the procedures for adjusting the
various components of the tape path - in particular, A/C head azimuth,
tilt, and height; and roller guide height. Before you attempt these,
you need to determine whether either of these are likely to be your
problems.
Symptoms of bad A/C head alignment
The following are some symptoms you may experience indicating the
need for A/C head adjustments:
Symptoms of bad roller guide height adjustment
The following are some of the symptoms you may experience indicating
the need for roller guide height adjustments:
Tape path alignment shifting over time
No, it isn't your imagination. Those wedding videos no longer play on your
VCR without adjusting the user tracking control even though you swear they
used to.
A/C alignment adjustment locations
While there are many variations on the exact locations of each of the A/C
head alignment adjustments, the following description is for one of the most
common layouts. See the appropriate sections elsewhere in this chapter for
the adjustment procedures for the A/C head.
Adjustment of A/C head - problems with tracking or sound (linear audio)
If the problems happened suddenly, it is probably not a misadjusted
audio/control head but some other mechanical fault - eliminate this
possibility before considering A/C head adjustments.
Roller guide height adjustment
You can do this by eye. Sophisticated test equipment and expensive test tapes
are not needed. One trick is of course not to mess with both guide posts at
the same time - but even if you do it isn't the end of the world.
This doesn't even require a scope - the video picture is an excellent alignment
tool! It does take patience and a steady hand.
Likely causes for sudden change in tracking behavior
If it is impossible to find a position of the user tracking control that
results in a stable picture, this section is for you. Some amount of the
picture may be noisy - top or bottom - or the tracking may be fluctuating
with a few second cycle.
Backtension adjustment
Most VCRs use a backtension band - a thin metal band with a felt liner -
to apply a carefully controlled torque to the supply reel during forward
tape motion in play, record, and CUE. A backtension lever or arm contacts
the tape as it leaves the supply side of the cassette and provides feedback
to control the tension on the backtension band and thus how much it resists
the rotation of the supply reel.
No, you don't need a fancy back tension meter
(From: Alan McKinnon (alan.mck@pixie.co.za).)
More on adjusting backtension
(From: Paul Weber (webpa@aol.com).)
VCR Sensors and Tape Counters
Tape start/end sensors
VHS cassettes use a clear leader and trailer for the purposes of detecting
beginning or end of tape. A light source that pokes up in the center
of the cassette illuminates photodetectors on either side of the cassette
through passages in the plastic passing through the tape as it leaves
and enters the cassette. This is shown in VHS Cassette
Showing Start and End Sensor Locations.
Start/end sensor testing
The start and end sensors are usually a combination of a light source
(IR LED) and IR photodiode. With a little effort, these can be tested
for functionality.
Tape counters
There are two kinds of tape position counters: reference and real-time.
Reel rotation sensors
Reel rotation is detected most often using optical sensors under the
reels though some older VCRs may use mechanical or optical interrupters
driven off of belts from the reel spindles. The optical approach is
depicted in VCR Reel Rotation Sensor.
Reel rotation sensor testing
The counters on some VCRs are active at all times - rotate the appropriate
reel and the counter will change (count up or down depending on its default
mode - the direction of rotation probably will not matter). If your VCR is
of this type, testing is particularly easy. Slowly rotate the takeup (usually)
reel by hand. The numbers should change several times - probably 4 - per
revolution. There should be no missed counts and there should be no positions
where the counter free runs - the display increments or decrements on its own
very quickly. Any of these could indicate a problem with the sensor or LED,
a buffer amplifier, bad connection, or the microcontroller or other IC that
actually drives the counter and display.
Stan's tips on reel sensors
(From: Stan Cramer (stvcrm@Gramercy.ios.com).)
Motors and Rotors
Types of motors in VCRs
There may be anywhere from 2 to 6 or more motors in your VCR. Some
designs use a single motor to power all functions except the video
head drum. Others have separate motors for each function. Most
typical are 3 or 4 motors. Motors perform the following functions:
Small brush-type permanent magnet (PM) DC motors similar to those found
in small battery operated appliances, CD and tape players, and toys
may be used for cassette loading and/or tape loading.
Testing and repairing small motors
Aside from obvious mechanical problems and lubrication if needed, you usually
cannot do much to repair defective motors. If you enjoy a challenge, it is
sometimes possible to disassemble, clean, and lubricate a motor to restore it
to good health. However, without the circuit diagram, even knowing what the
proper voltages and signals should be on (2) or (3) type motors would prove
challenging.
Capstan problems
Capstans are expensive especially if they are integral with the capstan motor,
but unless it is bent (very unlikely), or the bearings are totally shot, or it
is direct drive and the motor is bad, the capstan should not be a problem
as long as you **carefully** clean off all of the black tape oxide buildup
with alcohol and a lint free cloth or Q-tips. Don't get impatient and
use anything sharp! The black stuff will come off. A fingernail may
help. A dry bearing may need a drop or two of light oil (electric motor or
sewing machine oil). Sometimes, there is a bearing cover washer that works
its way up and interferes with the tape movement. Push it back down.
Some capstan motor information
(From: Mike Whitmore (whitmore@jila.colorado.edu).)
VCC - power to chip/motor- probably 9-12 V
FG - frequency generator output from motor to servo loop
CTL - control track pulse from Audio/Control head
F/R - forward/reverse (one high, one low)
Items of Interest
Why is a tracking control needed
In order for the video to be read off of the tape properly, the spinning
video heads must be centered on the very narrow diagonal tracks. The
width of these tracks is as small as .019 mm. The actual reference point
is not on the video heads but the A/C head - several inches away. The
control pulses put down during record are used to phase lock the capstan
to the spinning video heads. The distance between the control head and the
video heads determines whether the required centering will be achieved. In
the ideal world, the distance would be identical for all VHS VCRs - that is
the goal. It is part of the VHS specification.
VCRs with 2, 4, 6 or more heads - what is the difference?
A single pair (2) of heads is needed for basic record and playback. With
more heads, various aspects of these functions can be optimized to improve
picture quality - usually for the special effects like CUE and REV. For
example, a 4 heads are usually needed to produce decent quality playback in
CUE and REV modes for SP recorded tapes.
Which combination of heads are used for what modes?
The quick answer is: "almost any combination which includes at least one head
of each azimuth angle on each side of the video drum" :-).
More on 6 head VCRs
(From: Paul Weber (webpa@aol.com).)
Choice of SVHS or high quality 4 (or greater) head VHS VCR
SVHS won't be better than a good 4 head (+2 HiFi) unless:
About VISS and VASS
I assume VISS stands for "VHS Index Search System" or something similar. In
any case, VISS and VASS provide the means to mark the start (usually of a
video segment so that it can be accessed quickly later on.
"How standard is this system? My Goldstar VCR has VISS and now I see
reference to an LXI brand with the same system. I've heard of other VCRs
with functionally similar features, but never had the opportunity to try
exchanging tapes. Do they use the same marks? When my Goldstar finally
bites the bullet (beyond my powers to resuscitate it), will the collection
of indexed tapes I've built up be useless, or will another VCR with indexing
features find the marks that Goldstar put on them?"
How does the "commercial skip" feature work?
(From: Matt Kruckeberg (sackmans@ndak.net).)
Old clunkers and the march of technology
It always amuses me to listen to comments about how anything older than
6 months (or 30 minutes) should be tossed in favor of some newer, more cheaply
made piece of crap. Yes, convenience features and HiFi audio have made newer
VCRs a lot nicer in many ways. But for time shifting and the kids, that
old clunker will do just fine, thank you. Some of the older VCRs will just
keep going and going and going and going with a cleaning and a few rubber
parts from time-to-time.
Comments on quality of consumer electronic equipment construction
(From: Stan Cramer (stvcrm@Gramercy.ios.com).)
Can I add an S-Video input to my VCR?
Possibly, but why bother? You will most likely be limited by the VCR's
circuitry anyhow.
Can a VHS VCR record single video frames at a time?
It would be nice if it were possible to output still frames from a PC,
for example, to record computer animation on video tape. This would permit
images to be generated slowly and then played back in real-time.
Controlling one or more VCRs from a PC
Here is one approach to using a PC to program multiple VCRs. Obviously,
the techniques described below can be extended to more complex functions.
Feedback could be added to inform the PC of end-of-tape or other fault
conditions.
Using a VCR overseas or vice-versa
Some VCRs and TVs may have a selector switch or be universal but you would
have to check the manual.
Differences in blank VHS tapes between US and Europe
The only difference between using a blank tape purchased in the US then
used in the UK is the playing time will be different ie, a T120 (2 hours)
from the US will have a longer playing/record time in the UK. This is due
to the different head drum speed i.e., 60 Hz (1800 RPM) and 50 Hz (1500 RPM).
Why is a special VCR needed for multiple video standards?
A VCR is not simply 'analog playback' in the same way that an audio recorder
doesn't care whether you record classical or rock. The VCR must synchronize
to the video timing and demodulate the luminance and chrominance information
in order to lay down the tracks on the videotape. There are enough
differences among world video formats that while technically possible (and
such multiformat VCRs exist) it is not automatic - or free. The video
timing and modulation techniques for video formats like NTSC, PAL, SECAM,
etc. are sufficiently different that additional circuitry is necessary to
handle multiple formats. In the U.S. at least, there is not enough demand
Recording HiFi audio only on a HiFi VCR
The use of a $2 T120 tape with a HiFi VCR permits the recording of up
to 2 hours of audio with near-CD quality.
Stereo output from VCR RF connector?
(From: Mike Appenzeller (Michael.W.Appenzeller@lmco.com).)
Dubbing only video and linear tracks on HiFi VCR
"Is it possible to rerecord the video (and linear audio) tracks but preserve
the HiFi audio?"
Can I use an Uninterruptable Power Supply (UPS) to retain the programming?
Some VCRs do not have much of a long term memory should there be a power
failure. Can a UPS designed for a computer system be used with these VCRs
so that all the programming (and possibly channel settings as well) are
not lost every time the power line burps?
Can a VCR be used for computer backup?
The answer is yes but I would not recommend it. In order to provide
reliable backup, totally error free storage and retrieval must be
guaranteed. This is a non-trivial problem given that the video tape
is an analog storage media prone to noise and dropouts. Redundant
information would need to be stored and sophisticated error detection
and correction circuitry must be included. By the time you are done,
the theoretical capacity of a T120 video cassette of, perhaps, 5-10 GB
is greatly reduced. Furthermore, you probably want somewhat rapid
random access and this **will** be very hard on a consumer grade tape
transport designed for movie viewing and time shifting of soaps.
How can I use an old deceased VCR as a sophisticated appliance timer?
First, you might be able to repair the VCR and prolong its life. Why are
you reading this section and considering such a transgression? Grrrr.
Can I control the tuner from a VCR using my PC?
Perhaps, you have this fantasy:
"I'm wondering if it's possible to take the tuning circuit (tuner and
associated circuitry) out of a VCR and somehow controlling it with a PC (say
through the parallel port), and then feeding the composite signal to the
input of a video capture card?"
What is a delay line and where is it used?
The question you originally asked might have been: What is this alien
looking thing in my VCR?
Comb filters in camcorders?
(From: Jeroen H. Stessen (Jeroen.Stessen@philips.com).)
What are photocouplers and how are they different than optoisolators?
You have probably been unable to sleep at times thinking about this subject!
Why are there so many different designs for VHS transports?
Don't expect an amazing answer - this is a set of questions.
Service center honesty?
After taking your totally dead VCR into an authorized service center, it is
a month and still no diagnosis. When pressed, they finally 'discover'
that a diagnosis has been made and the estimate is $80.
VCR repair saga - a shop that hasn't seen this FAQ
The following is a true story. It appears to be an example of incompetence
compounded by a lack of basic decency in dealing with the customer. The
indented quoted text is from someone who wishes to remain anonymous.
"Recently my 4-5 year old JVC HR-D910U (Hi-Fi Stereo) VCR stopped
loading tapes properly. More specifically, a rubber roller which is
lifted up and out of the way when the tape is ejected would come down
right on top of the tape after the tape was loaded. This occurred
because some metal guide, which moves as part of the loading sequence,
wasn't properly pulling the tape out of the way of the (downward
moving) roller. Other than this problem, the VCR performed normally:
i.e., if one manually moved the metal guide to pull the tape out of the
way and then hit "PLAY", the machine would behave completely normally
in all modes until the tape was ejected and another tape was loaded in."
"I took the machine to a local repair shop that seemed reputable (has
been in business for a long time, does the actual repairs for local
stores of a large consumer electronic chain, etc...)."
"After charging me a $30 estimation fee (to be used towards the repair
if I so chose), they concluded that there was something wrong with some
gear in the loading mechanism as well as the mode switch. The price for
the estimated repair seemed reasonable, and so I authorized them to go
ahead. To make a long story short, after about 2 months (!) of waiting
(they claimed to have had trouble getting the parts) they reported that
they had replaced the parts, but the VCR still did not work. In fact,
it now loaded properly, but didn't play well, and in general was
confused about what mode it was in. For example, after ejecting a
tape, the spindles that insert into the VHS tape cartridge would
continue to spin around (as if there were a tape in there in PLAY
mode)."
"Their claim was that now there was something wrong with the micro-
controller on the VCR and that it was putting out some sort of
incorrect voltages. Moreover, this problem was allegedly masked by the
earlier problems, and only became apparent after they had performed the
repairs they had done."
"In their estimation, the price of replacing the controller wasn't worth
it, and so they wanted to just give me the VCR back, with the repairs
that had already done (but keeping the $30 estimation fee)."
"The repair place speculates that some voltage spike must have injured
the controller which may have coincidentally resulted in the loading
problem. Or, another theory they proposed was that the loading problem
caused some motor to over-strain itself in some way which caused an
electrical problem which injured the microcontroller."
"My theory is that, since the VCR was normal other than the loading problem
described, they must have screwed the machine up during the repair, but
do not want to take responsibility for that fact, and after putting in
a couple dollars worth of parts are happy to keep the $30 "estimation fee"
themselves."
"So, is their version of the story even remotely possible? If not, I feel
that they destroyed a perfectly good machine with a minor problem and I'm
wondering what, if any, recourse I might have in this sort of situation."
Testing of IR LEDs
The only differences in testing between a visible and IR LED (or IR Emitting
diode - IRED) are that:
IR detector circuit
This IR Detector may be used for testing of IR remote controls, CD player
laserdiodes, and other low level near IR emitters.
Vcc (+9 V) >-------+---------+
| |
| \
/ / R3
\ R1 \ 500
/ 3.3K /
\ __|__
| _\_/_ LED1 Visible LED
__|__ |
IR ----> _/_\_ PD1 +--------> Scope monitor point
Sensor | |
Photodiode | B |/ C
+-------| Q1 2N3904
| |\ E
\ |
/ R2 +--------> GND
\ 27K |
/ |
| |
GND >--------+---------+
_|_
-
VHS physical tape format
The general arrangement of audio, video, and control information is shown
below for a VCR with stereo audio. This view is from the front (oxide side)
of the tape.
Top edge of tape
------- ------------------------------------------- --------
^ Right linear stereo .35 mm
| ------------------------------------------- --------__ (Guard band,
| ------------------------------------------- -------- .3 mm)
| Left linear stereo .35 mm
| =========================================== ========
| \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ <-- End of scan,
| \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ Bottom of picture,
1/2" \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ Right (takeup side),
12.7 mm \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ roller guide.
| \ Video with HiFi sound \ <-- Tape motion \
| \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ Left (supply side)
| \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ roller guide.
| \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ Top of picture,
| \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ <-- Start of scan.
| =========================================== ========
v Control track .75 mm
------- ------------------------------------------- --------
Bottom edge of tape
VHS specifications
Tape width: 1/2 inch 12.7 mm
Tape length: 240 meters, T120 - 120 minutes at SP speed, most common.
Other lengths up to T160 and perhaps more.
Tape speed: SP 1-5/16 ips 1.3125 ips 33.3375 mm/sec
LP 21/32 ips .6563 ips 16.6688 mm/sec
EP 7/16 ips .4375 ips 11.1125 mm/sec
(Newer NTSC VCRs tend to only support SP and EP/SLP for
record but will play at all three speeds. All PAL and SECAM
VCRs may only support SP and LP for play as well.)
Track pitch: .058 mm (SP)
.039 mm (LP)
.019 mm (EP)
Track length: 3.8 inches 96.5 mm
Writing speed: 229 ips 5.84 m/sec
Min wavelength: 1 micrometer (.000001 meter or .00004 inches)
Recording density: (SP) 34K transitions/sq. mm
Recording time: SP 120 minutes 2 hours
(T120 cassette) LP 240 minutes 4 hours
EP 360 minutes 6 hours
Drum diameter: 2.44 inches (VHS VCRs).
1.63 inches (VHS Camcorders).
Drum speed: 30 RPS 1800 RPM (NTSC at 30 frames/s)
Rotation: Counter-clockwise viewed from above.
Tape movement: Left-right viewed from front.
Heads (typ): 2 for normal recording/playback.
1 to 3 optional for SP freeze frame/slow motion, etc.
2 optional for HiFi audio.
1 or 2 optional for flying erase.
End sensing: Clear leader and trailer.
Brake torque: Supply forward = 450 - 650 g-cm
Supply reverse = 70 - 130 g-cm
Takeup reverse = 450 - 650 g-cm
Takeup forward = 70 - 130 g-cm
Back tension: 20 - 25 g.
Takeup torque: Play - 80 - 160 g-cm
FF - greater than 350 g-cm
Rew - greater than 400 g-cm
Lum. Carrier: 3.4 Mhz
Color sbcrrier: 629 kHz
Azimuth angles: +/- 6 degrees
Frame length: 7.7 inches 196 mm
Field length: 3.85 inches 98 mm
Line length: .0147 inches .3723 mm
Skew: SP - 1.5 H (sync tips align)
LP - .75 H
EP - .5 H (sync tips align)
Color Vector A head is + 90 degree/H
rotation: B head is - 90 degree/H
Luminance Specifications for various VCR technologies:
Type Video Resolution FM Deviation Freq. Range
--------------------------------------------------------------
VHS (240 lines) 1.0 Mhz 3.4-4.4 Mhz
SVHS (*) (400 lines) 1.6 Mhz 5.4-7.0 Mhz
Beta1 (250 lines) 1.3 Mhz 3.5-4.8 Mhz
Beta2/3 (240 lines) 1.2 Mhz 3.6-4.8 Mhz
SuperBeta (285 lines) 1.2 Mhz 4,4-5.6 Mhz
ED Beta (500 lines) 2.5 Mhz 6.8-9.3 Mhz
(*) The tape for SVHS must have a higher coercivity since the frequency is
higher (information more dense) and the demagnetizing forces are greater.
Linear audio .0384 inches 1 mm (mono, along top of tape)
track width: .0138 inches .35 mm (L or R stereo, R at top of tape,
.3 mm guard band between L and R)
Audio bias: 67 kHz
Control track: .0288 inches .75 mm (along bottom of tape)
Guard bands: .0059 inches .15 mm (linear audio track to video)
.0059 inches .15 mm (video to control track)
Video recording theory
The majority of maintenance and repair procedures on VCRs and camcorders
can be carried out without really understanding **how** the video magic
is performed. However, if you want to really get into the nitty-gritty
or are simply curious, then the following book is for you. However, you
probably want to find it at a library - the suggested retail price is $55!
Z. Q. You and T. H. Edgar
Prentice Hall International (UK), 1992
ISBN 0-13-945890-5, TK6655.V5Y68.
VCRs are both NTSC and PAL compatible?
(From: drblake (drblake@bellsouth.net).)
Smoke damaged cassettes
(From: xcuseus9@mail.idt.net)
Sour grapes?
The following appeared as a reply to a sincere request for help on the USENET
newsgroup sci.electronics.repair. The company is unknown and I have deleted
the email address - this sort of comment is usually not constructive. However,
I include it to provide all points of view. :-) :-( It isn't that the comments
are without validity - just the way they are presented.
"Why do people insist that they have the knowledge to repair something as
complicated as an electronic circuit when they can't even program a VCR??.
If you are not familiar with switch mode power supplies, don't attempt to
repair it. If you are attempting to repair it and know of the consequences
and are prepared to pay more for the extra damage you cause, or if your
prepared to purchase a new VCR then go for it. But just don't do it to try
to save a few bucks. Good luck in whatever you decide to do."
Setting channels on older VCR
Auto tune on a VCR 15 years old? You have to be kidding! These are typically
varactor tuners, not modern quartz synthesizers.
Another use for dead VCRs
(From: Mark Kinsler (kinsler@bobcat.ent.ohiou.edu).)
Notes on the Gemini/Rabbit video multiplier
This consists of an RF transmitter and one or more receiver modules to allow
a single video source (typically a VCR) to be sent to TVs in other rooms of
the house.
Service Information
Advanced VCR troubleshooting
If the solutions to your problems have not been covered in this document,
you still have some options other than surrendering your VCR to the
local service center or the dumpster. Fortunately, VCRs are among the
most popular of consumer appliances to be addressed by literature that
is readily available - at all levels of sophistication.
Web resources
Radio Shack has a nice web resource and fax-back service. This is
mostly for their equipment but some of it applies to other brands and there
are diagrams which may be useful for other manufacturers' VCRs, TVs, CD
players, camcorders, remote controls, and other devices.
Popular books on VCR maintenance and repair
There are a variety of books dealing with all aspects of VCR maintenance and
repair. All will cover the basic cleaning and rubber replacement. Some of
these only address mechanical problems (but, hey, this covers most failures)
while other are heavy into the basic recording theory and electronic
troubleshooting. Your local public library probably has some of these in the
electronics section - around 621.38 if your library is numbered that way.
Technical bookstores, electronics distributors, and the mail order parts
sources listed in this document carry a variety of these texts.
The following is a recent publication:
Robert C Brenner and Gregory R. Capelco
SAMS, a division of MacMillan Computer Publishing
11711 North College,Carmel, Indiana 46032
Richard C. Wilkins and Cheryl A. Hubbard
TAB Books, a division of McGraw-Hill, Inc.
Blue Ridge Summit, Pennsylvania 17294
PROMPT Publications (Howard W. Sams), 1-800-428-7267
ISBN #0-7906-1076-0. $19.95
David T. Ronan
Delmar/ITP publishers
ISBN # 0-8273-6583-7
(From: scott.holderman@mogur.com (Scott Holderman).)
Steve Thomas
Retail Book Sales, Worthington Publishing Co.
P.O. Box 16691-B, 6907-202B Halifax River Drive, Tampa FL 33687-6691
(Tel: 813/988-5751)
Gene B. Williams
TAB Books, Inc., 1992
Blue Ridge Summit, PA 17294-0214
ISBN 0-8306-4181-5 (paperback)
Author Date Title
---------------------------------------------------------------------------
1 Ronan, David T. 1995 Practical VCR repair
2 Wayne, Victor A. 1992 Operating your VCR.
3 Capelo, Gregory R. 1991 VCR troubleshooting & repair.
4 Wilkins, Richard C. 1991 Home VCR repair illustrated.
5 Thomas, Steve. 1990 How to keep your VCR alive.
6 Brenner, Robert C. 1987 VCR troubleshooting & repair guide.
7 Goodman, Robert L. 1996 Maintaining & repairing VCRs
8 Williams, Gene B. 1993 All thumbs guide to VCR's.
9 Goodman, Robert L. 1993 Maintaining and repairing VCRs.
10 McComb, Gordon 1991 Troubleshooting and repairing VCRs.
11 Williams, Gene B. 1990 Guide to VCRs, camcorders, & home video.
FCC ID Numbers of VCRs
Only a few manufacturers actually produce the vast majority of VCRs. For
example, Radio Shack, Magnavox, and Emerson do not make their own VCRs (I
can tell you are not really surprised!). Or, how about a brand of 'Pulsar'
sold through a store chain with the name of Canadian Tire? Rubber companies
really do not design VCRs (even if there is something inside a VCR called an
idler tire. :-)
ORIGINAL UL LISTED FCC LISTED
MANUFACTURER CODE(s) CODE(s)
Akai 186Z ASH
Daewoo 41K4 C5F
Fisher/Sanyo 403Y AFA
Funai 333Z, 51K8 ADT, EOZ, BFY
Goldstar 86BO BEJ
Hitachi 238Z ABL, AHA
JVC 439F ASI
Matsushita (1) 679F ACJ, AIX, AJU
Mitsubishi 536Y BGB
NEC 781Y A3D, E74
Orion-Emerson 44L6, 722 A7R
Philips (2) 645Y BOU
Samsung 16M4, 414K A3L
Sharp 504F ATA, APY
Sony 570F AK8
Toshiba 174Y, 84X7 AGI, G95
564. - Sanyo/Fisher
565. - Sanyo/Fisher
934. - Hitachi
580. - Goldstar
274. - RCA
626. - Phillips (Mag)
Determining belt, tire, and pinch roller specifications
Belts are normally specified by their cross section - square, flat, round,
and their inside circumference (IC). The IC is used since it is virtually
impossible to accurately measure the diameter of a belt.
About decayed tan or brown glue on circuit boards and leaking capacitors
Larger components like electrolytic capacitors are often secured to the
circuit board with some sort of adhesive. Originally, it is white and
inert. However, with heat and age, some types decay to a brown, conductive
and/or corrosive material which can cause all sorts of problems including
the creation of high leakage paths or dead shorts and eating away at nearby
wiring traces.
Where did all the adjustment go?
Like TVs and monitors, newer VCRs have much more of their adjustments done
digitally inside complex integrated circuits. What this means is that there
may be no easy way to tweak some of the common parameters without either
a special remote control or a computer interface and software. Good for the
manufacturer; bad for the DIYer and even professional repair person.
"Does anyone know which variable resistor adjusts the head switching point in
a Sony CCD-F401 camcorder, where it is?"
Interchangeability of components
The question often arises: If I cannot obtain an exact replacement or
if I have a VCR, tape deck, or other equipment carcass gathering dust, can I
substitute a part that is not a precise match? Sometimes, this is simply
desired to confirm a diagnosis and avoid the risk of ordering an expensive
replacement and/or having to wait until it arrives.
Suggested Parts Suppliers
For general electronic components like resistors and capacitors, most
electronics distributors will have a sufficient variety at reasonable
cost. Even Radio Shack can be considered in a pinch.
Studio Sound Service (Rebuild kits for many popular VCR switchmode
power supplies, VCR parts, some components.
U.S. Fax: 1-812-949-7743 They will be happy to identify specific VCR
Email: part numbers as well based on model and
studio.sound@datacom.iglou.com description as well - see below.)
Web: http://www.iglou.com/studiosound/
VCR service parts and assistance for the do-it-yourselfer
(From: Frank Fendley (studio.sound@datacom.iglou.com).)
Used VCR parts
Perhaps they would get more respect if they were called 'previously owned'
or 'broken-in' VCR parts. :-)
368 Ball Hollow Road
Pulaski, Tennessee 38479
Phone: 1-615-427-6262
Email: allbrand@juno.com
Web: http://www.usedvcrparts.com/
Other Sources
(This section from: ac557@detroit.freenet.org (Ted C. Gondert).)
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