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Does 'blank picture' means a totally black screen with the brightness and contrast controls having no effect whatsoever? Or, is there is no picture but there is a raster - light on the screen? The direction in which troubleshooting should proceed differ significantly depending the answer. Verify that you computer has not simply entered power saving mode and blanked the screen or shut off the monitor video and power circuits entirely. Confirm that the video source is not defective or blank - try another one. Here are some questions: 1. Is there any light on the screen at any settings of the brightness and contrast controls, and/or when switching channels. Can you see any raster scanning lines? 2. Can you obtain a raster of any kind by adjusting the screen (G2) control (probably on the flyback) or master background or brightness? 3. Looking in the back of the monitor, can you see the glow of the CRT filament? 4. Do you get that static on the front of the tube that would indicate that there is high voltage? Any cracking or other normal or abnormal sounds or smells? If the answer to all of these is 'no', then you have a power supply and/or deflection problem. Refer the the section: "No picture but indications of power". Possible causes of no raster: * No or low high voltage (low voltage, deflection, or high voltage power supply failure). * Fault with other voltages like G1 or screen (G2) to CRT. * Filament to CRT not getting powered. * Drive to CRT bad/shut off as a result of fault elsewhere. For example, failure of the vertical deflection may disable HV or blank the screem to protect the CRT from burn-in due to the very bright horizontal line that would result. With some monitors, it is possible that the X-ray protection circuitry will blank the screen. Possible causes of no video: problem in video input, video amplifiers, video output, cutoff due to other fault. It could be as simple as a bad connection - try gently prodding the boards with an insulated stick while watching the screen. Check for loose connectors and reseat all internal connectors.
The following assumes that the picture is fine but the brightness is fixed - probably at too high a level. However, there could be several interrelated problems if a common supply voltage were missing, for example. If it is a knob, then it should be varying the control grid (G1) voltages relative to the cathodes (K) of the CRT. This is not likely to be a very complex circuit. If you do not have a schematic, I would start by tracing from the control, check continuity and solder connections. Check the control itself for proper operation with an ohmmeter. A power supply going to one side of the control (negative probably) may be missing. Tbe control grid voltage will end up on the little board on the neck of the CRT - check there as well for bad solder connections or open resistors. If brightness is a digital control, then you will need a schematic unless there is an obvious bad connection.
This means absolutely no color - equivalent to a black and white picture. Not even a hint of color. If you are using a composite video input, troubleshoot the chroma circuitry like you would a TV - see the document: "Notes on the Troubleshooting and Repair of Television Sets". This is an extremely unlikely failure mode for a computer monitor unless you are using a composite video input. It is most likely to a software driver or program problem. Sometimes, the PC will think that the monitor you have connected is not capable of color and certain programs will then display in B/W no matter what. In some cases this is due to an initialization problem - possibly a race condition during the boot process - especially likely if you are using an older video card with a new fast processor. First, confirm that the source is actually in color - try the monitor on another computer or vice-versa. Check the settings of any mode switches - in rare cases there is a color/mono switch or button. Note that to the average person, the obvious question becomes: is my color picture tube bad? The answer is a definitive NO. It is virtually impossible for a defective CRT to cause a total loss of color. A defective CRT can cause a lack of a primary color - R, G, or, B which will mess up the color but is not likely to result in a black and white picture.
If the problem is slight and/or has gradually gotten worse, this may just require an adjustment of the color brightness/background/bias and/or color gain/drive controls inside the monitor. See the section: "Brightness and color balance adjustment". Even if it appears as though there is an excess, this may actually be a reduction in one of the primary colors. For example, a magenta tinge is represents a reduction in the strength of the green signal. * Too high an intensity for one of the color channels will result in a tint of one of the primaries: red, green or blue. * Too low an intensity for one of the color channels will result in a tint of the complement of one of the primaries: yellow, cyan, or magenta. * Problems mainly in the shadows or dark areas of the picture usually represent a fault with brightness/bias/background. * Problems mainly in the highlights or bright areas of the picture usually represent a fault with the gain/drive. A color that that is now suddenly brighter or darker than normal resulting in incorrect color balance or a tint in the background could be due to a number of causes: * Bad cable or pin bent on cable connector. * Bad connections or bad component in video amplifier or on CRT neck board for that color. * Weak gun in CRT (reduced color). * Bad video card or incorrect software color map settings. * For monitors with sync-on-green capability, the monitor may think you are using sync-on-green when in fact you have separate sync. In particular, this may result in a problem with excessive green: (From: Bob Myers (myers@fc.hp.com)). Some monitors provide a user-selectable setup option for "sync-on-green" vs. separate syncs. Sometimes, this doesn't really change where the sync itself is coming from. In those cases, it's automatically detected but *does* change where the reference level for the video is expected to be. You might try checking this setting, if you have it, and changing it back and forth to check the effect. It's not likely to be the problem in a separate-sync system like a PC, but weirder things have happened and it's easy and cheap to check out.
The means colors that are not normal and that adjustment of the user controls is not able to correct it so that all colors of the picture are properly displayed at the same time. For example, you are unable to get any yellows or blues in picture that should have these colors. * If you are using a composite video input, troubleshoot the chroma circuitry as you would a TV - see the document: "Notes on the Troubleshooting and Repair of Television Sets". * Confirm that the input is not a weird color video - try another software program or video source. We have a draftsperson who always sets up his Windows color scheme in this manner - we keep wishing it is the monitor as **that** could be fixed! * Verify that this is not a missing color problem - one of the primary R, G, or B, has disappeared. If so, refer to the section: "Intermittent, flickering, or missing colors". * If this is a monitor with BNC connectors and you are using them, make sure you had the video termination switches set correctly (75 ohms if this is the only monitor or the last monitor in a daisychain; HiZ if an intermediate monitor in a daisychain.) A very common cause of unbalanced or blooming colors assuming the monitor itself is good is incorrect settings of the termination. * A bad connection, bad component, or short circuit in the video circuitry or CRT neck board could also result in strange colors.
Any intermittent problems with monitors that cause random sudden changes in the picture brightness, color, size, or position are often a result of bad connections. Bad solder joints are very common in monitors due both to poor quality manufacturing as well as to deterioration of the solder bond after numerous thermal cycles and components running at high temperature. Without knowing anything about the circuitry, it is usually possible to cure these problems by locating all bad solder connections and cleaning and reseating internal connectors. The term 'cold solder joint' strictly refers to a solder connection that was either not heated enough during manufacturing, was cooled too quickly, or where part pins were moved before the solder had a chance to solidify. A similar situation can develop over time with thermal cycling where parts are not properly fastened and are essentially being held in by the solder alone. Both situations are most common with the pins of large components like transformers, power transistors and power resistors, and large connectors. The pins of the components have a large thermal mass and may not get hot enough during manufacturing. Also, they are relatively massive and may flex the connection due to vibration or thermal expansion and contraction. These problems are particularly common with TVs and monitors - especially cheaper monitors. To locate cold solder joints, use a strong light and magnifier and examine the pins of large components for hairline cracks in the solder around the pin. Gently wiggle the component if possible (with the power off). Any detectable movement at the joint indicates a problem. With the power on, gently prod the circuit board and suspect components with an insulated tool to see if the problem can be effected. When in doubt, resolder any suspicious connections. Some monitors may use double sided circuit boards which do not have plated through holes. In these cases, solder both top and bottom to be sure that the connections are solid. Use a large enough soldering iron to assure that your solder connection is solid. Put a bit of new solder with flux on every connection you touch up even if there was plenty of solder there before. However, remove any obvious excess. Inspect for solder bridges, sliver, splashes, etc. before applying power.
I can think of several potential reasons - all solvable but at higher manufacturing cost. 1. Mass of large component leads (like shields) does not get adequately heated during manufacture leading to latent cold solder joints. While they may look ok, the solder never actually 'wetted' the heavy pins and therefore did not form a good mechanical or electrical bond. 2. Thermal cycles and differential thermal coefficients of circuit boards, traces, and solder. While it is not easy to do anything about the material properties, using plated through-holes or a similar mechanical via would greatly increase the surface area of the joint and prevent the formation of cracks. 3. Vibration. This is also directly related to the single sided circuit boards without plated through-holes to strengthen the joints. 4. Lack of adquate mechanical support (single sided circuit boards without plated through-holes (vias). I believe that the single most significantimprovement would come about by using plated trhough-holes but this would add to the cost and apparently the consumer is not willing to pay more for better quality and reliability! Some designs have used rivlets - mechanical vias instead of plated ones. While this is good in principle, the execution has often been flawed where cold solder joints resulted between the rivlets and the circuit board traces due to lack of adequate process control. Monitors, due to their generally higher cost compared to TV sets, should be better constructed but not always.
This is a catch-all for some of the most common monitor problems. Most of
the causes boil down to bad connections of one form or another. However,
defective components like bias resistors on the CRT driver board or in the
video circuitry could also be at fault.
* Does whacking the monitor have any effect? If so, then bad connections
are confirmed. If the color(s) come and go suddenly, then it is most likely
*not* a CRT problem. The bad connections could be at the VGA cable, video
driver board on the neck of the CRT, or elsewhere (see below).
* If the color fades in and out with a delay of about 10-15 seconds, it is
probably intermittent power to the CRT filament for that color and probably
means a bad CRT since the three filaments are wired in parallel inside the
CRT. One of the internal connections has come loose.
Look in the neck of the CRT to make sure all three filaments are glowing
orange. If one is out or goes on and off, toss the monitor. Replacing the
CRT is probably not worth it. However, if they all go on and off together
(all colors would be fading in and out though perhaps not quite in unison),
then bad connections for the CRT filaments on the CRT neck board are
indicated.
Possible causes of intermittent or missing colors:
* VGA or other video input cable. Sometimes these develop intermittent
problems at the connector to the VGA board. These may be internal
to the cable in which case it will need to be replaced or if you are
handy and have infinite patience, you can replace just the VGA connector.
Alternatively, the male pins of the cable may not be making good contact
with the female VGA socket. First try contact cleaner. If this does not
work, gently squishing the male pins with a pair of needlenose pliers may
provide temporary or permanent relief if the pins are a tad too small.
However, if you go too far, you can damage or break the pins or cause the
female socket to become enlarged and loose fitting for any other monitor
you may use.
If this just happened after reconfiguring your system and reconnecting
the monitor or installing a new monitor, check your video connector - you
may have bent over or pushed in pins 1, 2, or 3 - the R, G, and B video
signals respectively.
If you find a bent pin, ***carefully*** straighten it with a pair of
needlenose pliers. If it is pushed in, try to grab onto it and pull it
out - then put a drop of Epoxy or other adhesive at its base (don't get
any on the part of the pin that makes contact) to prevent it from being
pushed in again.
There may be cold solder joints on the VGA board itself at the VGA
connector. These can be resoldered.
* Printed circuit board on the CRT neck. This is a common location for
cold solder joints. Check with a bright light and magnifying glass
for hairline cracks around the pins of larger parts. Prod and tap with
an insulated tool to see if the problem is effected. Resolder if necessary.
* Cold solder joints elsewhere in monitor usually around the pins of
large parts such as transformers, power transistors and resistors, and
internal connectors. Inspect with a strong light and magnifier if
necessary.
* Internal connectors that need to be cleaned and reseated. Remove,
clean with contact cleaner, burnish, and replace.
* Bad filament connections inside the CRT (gradual fade in and out or
one filament not lit). Replace CRT or monitor.
To narrow down the problem:
* Locate the output for the bad color on the video driver board on the
neck of the CRT. This will probably read a significantly higher
voltage than the corresponding pins for the good colors. A circuit
problem is likely - probably on this board but it could be in other
parts of the video circuitry.
* Test components on this board for the good and bad color channels. A
shorted transistor or open resistor can kill one channel. Swap parts
between good and bad colors to confirm.
* Gently pull the CRT neck board off of the CRT and replace it. This will
tend to clean the contacts.
* Connect an output of the video circuit/chip that is working (i.e., a color
that appears on the screen) to *all* three color drivers on the CRT neck
board.
- If you now get a more-or-less black and white picture (there may be a
moderate color tint as the relative intensities of R,G,B may not be
balanced), the problem is likely with the circuitry on the mainboard.
Note: the picture will be the intensity of only one color channel so it
will not be quite *normal* in any case.
- If you still have missing or messed up colors, the problem is on the CRT
neck board or with the CRT.
Anytime that intermittent symptoms are experienced, I recommend gently whacking the patient to determine if mechanical shock or vibration affects the behavior. Here are a couple of responses to this suggestion. (From Marc Gelfond (71363.1700@CompuServe.COM)): I just love the bit about "whacking it". It brings to mind an episode from the old Andy Griffith show, where a new fangled piece of electronics gear, was broght into Emmets repair shop. After many long hours of fruitless troubleshooting, out of frustration Emmet gave the thing a whack, and sure enough it fixed the problem. As we say in the Telephony business, it "CCWT" or Came Clear While Testing.Another saying is that it "CCBFM" Came Clear By F------ Magic!! (To which Gavin Adams (gaa@hopi.com) comments): In the video industry we had a saying concerning malfunctioning gear: "If it's broke, hit it with a hammer" "If that doesn't fix it, paint it and sell it" My DEC 16" monitor is case in point. Evey once in a while it would lose sync, and smacking it would bring it back (sometimes a few smacks). Recently it gave up the ghost completely, and after the local DEC office gave me a quote of $900 to fix it (Bermuda), I ordered a new Viewsonic 17" for the same price. I ripped the guts out of the DEC beast, painted it with a marble finish, put plants in it, and sold it! :>
Complaints about these kinds of problems are very common especially as the screen resolution and necessary video bandwidth keeps increasing. Most are due to cable and video termination deficiencies and not actual monitor defects. The video signals for red, green, and blue (or just a single signal for monochrome) are sent over cables which are generally 75 ohm transmission lines. These are coaxial cables that may be combined inside a single sheath for VGA, SVGA, MACs, and many workstations but may be separate coaxes with BNC (or other) connectors for other video applications. Without going into transmission line theory, suffice it to say that to obtain good quality video, the following conditions must be met: 1. A good quality of cable must be used. This means one in which the characteristic impedance is close to the optimum 75 ohms, one which has low losses, and one which has good shielding. For installations using BNC connectors, a good quality of 100% shielded RG59U is often used. The BNC connectors must be properly installed or they will contribute to mismatch problems. 2. Where multiple monitors are to be connected to a single video source, all wiring is done in a daisy chain fashion. The only taps permitted are the minimum necessary to connect each monitor to the chain. This usually means a BNC-T connector or a pair of connectors on the monitor for each video signal. T connections with cable must be avoided. 3. Only the last monitor in the chain should be terminated in 75 ohms. All of the others must be set to Hi-Z. Monitors with BNC connectors will usually have one switch or a switch for each color to select termination. Monitors for PCs, MACs, and workstations usually have built in termination and do not offer the choice of Hi-Z. This means that without a video distribution amplifier, it is not possible to connect multiple monitors of this type to a single video source with any expectation of a good quality display. Failure to follow these rules will result in video ringing, ghosts, shadows, and other unsightly blemishes in the picture. It is often not possible to control all aspects of the video setup. The cable is often a part of the monitor and cannot easily be substituted for a better one. The monitor may not have properly designed circuitry such that it degrades the video regardless of the cable and display board quality. The display card itself may not have proper drivers or source termination. Ironically, the better the video card, the more likely that there will be visible problems due to termination. This is due to the very high bandwidth and associated signal edge rates. Some examples of common termination problems: * Overly bright picture with trails following vertical edges, perhaps with periodic ringing. This is due to a missing termination. Check if the monitor is set for Hi-Z instead of 75 ohms. If there is no switch, then the termination may be faulty or the monitor may need an external resistor. For BNC connectors, plug-on terminations are available. * Bright ghost images adjacent to vertical lines. This may indicate that the terminating resistor is greater than the impedance of the cable. You may be using Ethernet Thinnet cable by accident which is RG58 with an impedance of 50 ohms. * Dark picture and ghost images adjacent to vertical lines. This may indicate that the terminating resistor is too low - multiple monitors on a chain all set for 75 ohms instead of just the last one. Or, an improper type of cable such as audio patch cord. * Fuzzy vertical edges. This may indicate a poor quality cable or a run which is just too long. For high resolutions such as 1280x1024, the maximum cable length may be as short as 25 feet or less for poor quality cable. Better cable or fiber-optic repeaters may be necessary. * Other similar problems - check cables for defective or improperly installed connectors. This is especially applicable to cables with BNC or UHF type connectors which require a kind of artistic talent to assembly properly and consistently. If only 1 or 2 colors (of the R, G, and B) are effected, then look for improper switch settings or bad connections (bad cable connectors are really common) on the problem color cables.
The problem is that on a white background the various objects leave a shadow to their right. Not a duplicate image but more like horizontal dark streaks on the white background. Also it seems that high intensity colors display very bright but low intensity colors are overly dark (almost black). The contrast and brightness adjustments may make no difference. This could be a number of things but they are all in the video amplifier and probably not the CRT driver board though this is possible. Dried up filter capacitors could result in video dependent ripple on the power supply lines. Bad coupling capacitors could result in similar symptoms but probably for only one color, not all of them. Since all colors are effected, look for something common like a bad power supply. With a scope, this would probably be rather easy even without schematics. If the brightness and contrast controls do nothing, this would suggest some fault in their general area or the IC or transistors they control in the video amps - and that this is not a CRT problem. Locate the video amp IC if it uses one and locate a pinout - this should be enough to determine which signals are faulty. First, do check carefully for bad connections and other obvious failures. This could also be a symptom of a bad CRT but this would be unusual with a not-ancient monitor (and not if the brightness and contrast controls have no effect).
If you can obtain a full intensity raster by varying the brightness or screen control, then your problem is most likely in the video amplifiers or power for the video amplifiers. If, however, the screen control varies the brightness but will not get a bright raster, you probably have problems either with the HV power supply or the filament supply for the CRT - is there the normal bright orange glow at the base of the CRT? If it is dim or very reddish, there may be a marginal connection or bad component in the filament circuitry.
During the time the electron beam is returning from right to left at the end of a line and bottom to top (over the course of multiple lines), it is supposed to be result in no visible light on the screen. However, a number of faults can result in visible retrace lines. The appearance will likely be a general reduction in contrast from the visible horizontal retrace on every scan line and two dozen or so diagonal lines lines (lower left to upper right) resulting from the vertical retrace. The retrace lines may be either white or gray (possibly with a slight color tint due to unequal settings of the color adjustments) or a primary color - red, green, or blue. Anything in between is also possible but less likely.
Where all colors are involved - the lines are essentially white or gray (or with a slight tint due to slight unequal settings of the color adjustments), look for something common like an incorrectly adjusted screen (G2) or master brightness/background/bias control or a problem in one of these circuits, a defective power supply or a problem in the blanking circuitry: * Screen (G2) or master brightness/background/bias control - mark setting and then see if a slight adjustment removes the retrace lines. See the chapter: "Monitor Adjustments". Of course, if this happened suddenly, the problem is not due to a misadjusted control though a dirty pot is possible - turn it back and forth - this might clean it and restore normal operation. * Power supply or connection to CRT neck board - insufficient voltage will result in the CRT never totally blanking. Check (usually scan derived) power supply components (from flyback). * General power supply - check B+ for correct value and ripple. A main power supply fault might result in these symptoms (and usually many others). * Blanking circuit - this may be a part of the video/chroma chip or separate. Check waveforms to determine if the blanking pulses are making it to the video output.
Where only one color is showing, suspect an incorrectly adjusted individual background/bias control or bad part on the CRT neck board for that color. * Individual brightness/background/bias control(s) - mark setting of pot for the problem color and then see if a slight adjustment removes the retrace lines. See the chapter: "Monitor Adjustments". Of course, if this happened suddenly, the problem is not due to a misadjusted control though a dirty pot is possible - turn it back and forth - this might clean it and restore normal operation. * Component or connection on CRT neck board - insufficient voltage to or incorrect biasing of the video driver for this color can result in the CRT never totally blanking. Compare voltages and signals, and swap components between good and bad channels to confirm. * Blanking circuit - this may be a part of the video/chroma chip or separate. Check and compare waveforms of good and bad colors to determine if the blanking pulses are making it to the video output. There is a slight possibility that a bad CRT may result in visible retrace lines. To eliminate this possibility: * Disconnect the filament - all evidence of a picture, raster, and retrace lines should disappear once the filaments/cathodes have cooled (15 seconds or so. If there are still visible retrace lines, the CRT is suffering from cold or field emission from someplace (may not even be the cathode). * Turn down the screen (G2) control on the flyback (usually). If one color remains no matter how you set the control, again there is some kind of weird emission from the CRT. However, if white/gray retrace lines remain, the problem may be in the screen supply. See the section: "Bad CRT causing retrace lines".
(From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). The TV which I bought last started developing retrace lines after a month or so of use. I took it back to the lab for warranty (special deal) and had it examined by the real experts. They found that even with the filament supply disconnected and VG2 at 0V the screen would still light up. They could even see that the electrons weren't even coming from the cathode. That was with only the picture tube in a test rig. So in this case the obvious conclusion had to be that the tube was bad, and it was replaced (32" 16:9 SF, very $$). It had something to do with processing problems during manufacturing of the electron guns. So even if this was a rare case, it *can* happen that retrace lines are due to a bad picture tube. It's more usual to suspect the VG2 (screen voltage) or a defect somewhere in the RGB video path.
This could be a heater-cathode (H-K) short in the CRT or a failure
of a component in the chroma circuits or video output (driver board).
Don't panic - heater-cathode shorts in CRTs can often be worked around.
Note: before proceeding, it is a good idea to make sure that the screen is
degaussed - else you could be attempting to track down problems with the wrong
color!
Some simple tests can confirm or rule out other possibilities.
* Compare the voltages for the video drive signals to the CRT on the little
board on the neck of the CRT with the CRT both connected and unplugged.
A schematic will help greatly in locating these signals.
- If there is a significant difference especially on the bad color, then the
CRT is a likely candidate. Try tapping the neck of the CRT GENTLY (with
it plugged in and while viewing a picture) to see if it is an intermittent
problem.
- If there is no significant difference, you may have a bad driver or a
problem in the chroma circuits.
* Look for bad connection/cold solder joints, probably on the little
board on the neck of the CRT. Use an insulated stick to gently prod
the board and its components in an effort to induce/cure the problem.
Look carefully for hairline cracks around the component leads.
* You can swap components between two colors and/or test with an ohmmeter
on that driver board to determine what is bad. The nice thing about
color monitors and TVs is that there three copies of each of these
components. Swapping and/or comparisons between these is an excellent
diagnostic technique.
* Another simple test: Disconnect the cathode for the full-on color from its
drive. If it is still full-on, there is probably an H-K short in the CRT
since the only way to get each color on the screen is via the cathode
connection to the CRT neck board. If it is removed and there is still that
color, the current must be taking another path inside the CRT.
* Alternatively, interchange the outputs of the bad color with a good one
by jumpering on the video driver board (on the CRT neck). If the bad
color changes, then the problem is in the circuitry and not the CRT.
Here is the procedure in more detail (example for red full on):
(From: J. K. Emerine (jkemerine@aol.com)).
To identify if the fault is in the crt or a control problem try this (WITH
SET OFF):
On the CRT board, lift the output end of the green cathode final resistor.
Do the same with the offending red cathode's resistor. Use short insulated
jumpers to 'swap' drive signals - drive the red cathode with the green
drive and the green cathode with red drive. (Note that if this problem
only occurs after a warmup period, color at turn on will be - well - wierd,
but it is just a test.)
- If the symptom returns = 'goes red' the CRT is shorting. (See the section:
"Providing isolation for a CRT H-K short". --- sam)
- If instead the symptom becomes 'goes green' then the red drive leg has
the fault and the CRT is probably good. (In this case, there may be bad
connections or a bad component on the CRT drive board or further back
in the chroma circuitry. --- sam)
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