Fixing "snapped/broken" DC2xxx/DC6xxx tapes

• 1. About the Author & Copyright
• 2. Summary
• 3. How does the tape work
• 4. What goeth amock
• 5. Quick fix (for the tape drive)
• 6. "Save Thy Ass"
• 7. Hint
• 8. Fix it
•   8.1) Procedure
• 9. Lesson

1. About the Author & Copyright

• No fee is charged
• Distribution outside the Internet and WWW is by prior permission
• This header is included unchanged

2. Summary

Besides, these tapes aren't exactly quot;inexpensive" either...

3. How does the tape work

Since the data on the tape is of great value and needs to be reliably read off for long periods of time, the cartridge is designed with reliability and quality in mind.

• The base of the tape is fashioned from a slab of aluminum. It not only provides a sturdy base for the steel guides and spool axles but also serves as a heat dissipator. Heat is generated wherever there is friction - the axles of the spools, the head rubbing the tape, and friction of the tape against the fixed guides. Heat, as you may realize, is detrimental to the tape's life and data-storage reliability. For example, the tape stretches more easily when it is hot - in fact, it may really snap!

• Various steel guides and rollers steer the tape from one spool to the other. Alignment is critical as the whole design of the cartridge relies on the fact that both the tape and the tensioning/drive belt are always within specifications.

• The transparent upper-case is made of very rigid and durable plastic which not only adds strength to the case but also serves to center the metal guides and rollers. The upper-case also has a movable door which protects the tape surface from the elements when the tape is out of the drive yet allows the read/write head access when the tape is inserted into the drive.

• The tensioning/drive belt is really something. I believe it was developed by 3M. It has to survive constant abuse and yet not loose its elasticity - the same can not be said of the common rubber band which crumbles to dust in a few months! This drive-belt is moved by the drive wheel and transfers this motion to both tape spools - making sure that they turn appropriate amounts - keeping the tape tension even.

• Unlike standard cassette tapes, where the magnetic medium is physically attached to both spools, the DC2xxxx/DC6xxx tapes use a completely different means of sensing when the rewind and fast-forward functions have completed. The tape has 3 to 4 sets of groups of small holes at both ends of the tape. These groups of holes are about one foot apart on the tape. The cartridge has a 45 degree "mirror" made of silvered plastic that provides a way to view the presence of these holes from the top and front of the tape.

  (Trivia: some drives sense the distance between the holes and can determine the capacity of the tape!)

  The front of the tape looks like this:

  
         +-----------------------------------+
         | door     drive          |mirror|  |
         +-----------------------------------+
  

  The side view:

  
                                     light source (LED)
  					 ||
         +------------------------------------+
         |                                 \ T| -> detector
         +------------------------------------+
  

  Where the "\" is the mirror and "T" is the tape.

  The light source has now been replaced with an IR (InfraRed - 900nm or so) emitter and an IR detector. These have many times the life expectancy of the old light bulb and CdSe (Cadmium Selenium photo-resistor) as well as much faster response.

  As the tape rolls by, the sensor "looks" for light. This light only comes when the small holes in the tape scroll by! And this is how the tape drive knows when it is at the start or end of the tape. Oh, the group of holes at the start of the tape is known as BOT (Beginning Of Tape) and the end is known as EOT (End Of Tape).

4. What goeth amock

DUST blocks the sensor such that the controller NEVER sees the light though the holes at BOT or EOT. Since the tape is NOT physically attached to the spools, it simply rolls off!!!

Note: In some rare cases, a part of a label may have peeled off and stuck to the internals of the drive. In these cases, skill with a thin, flat screwdriver will come in handy - as you must get that crud out of the drive. Only other way is to take it apart - which I do not recommend as these tape drives are made to be put together ONCE and tend to break SOMETHING during [dis]assembly. Hey, what do you want for < $200?

The dust problem applies to almost all PCs which have a fan in the power supply which forces air out... The problem is that this air has to come from somewhere. While some of it does use the intended ventilation slots, a sizable amount chooses the path of least resistance. This is usually the floppy drives, the tape drive, and any other devices which permit free airflow from the outside.

5. Quick fix (for the tape drive)

This should dislodge any dust in the path of the light beam so that the BOT and EOT are correctly sensed. This is only a TEMPORARY solution as the dust soon begins to accumulate again...

There are no easy solutions to the dust-accumulation problem but Dave Fanger suggests the following:

"I have kept a piece of polyurethane foam, cut to the size of a tape cartridge, jammed in the drive to inhibit and filter any air that passes through. Seems to work fine."

6. "Save Thy Ass"

My warranty to you: If you find that you have received an incomplete or garbled collection of sentences and paragraphs, you can connect to my WWW server and get a FREE replacement! The above paragraph will apply to that copy also. Happy? You better be ;-)

7. Hint

8. Fix it

• Well lighted, clean, & flat table
• Small, good quality, phillips (+) screwdriver
• Toothpick or a Q-tip or UNMAGNETIZED tweezers
• Small cup/drawer/container for the screws
• At least 6 hours of sleep the night before (VERY IMPORTANT!)

  8.1) Procedure

• Wash your hands. No grease/dirt allowed! I mean it.
• If you have poor eyesight/hand coordination, STOP NOW.
• Most DC2120 tapes have 2 screws on the bottom and 3-4 plastic barbs. Remove the 2 screws and put them in the container.
• Hold the tape at the edges so that your fingers hold BOTH the plastic case AND aluminum base. With the screwdriver, pry the barbs out of the aluminum holes so that the shell and base separate. DO NOT COMPLETELY SEPARATE THE BASE FROM THE SHELL. Optimally, the barbs only have to RELEASE.
• Lay the tape, BASE down on the table with the drive wheel facing you.
• While holding down the aluminum BASE (from both sides), remove the top shell. WATCH THE ACCESS DOOR CLOSELY. ALSO, be sure the case does not catch any rollers and send them off the table (and into never-never land...)
• Lay the plastic case out of the way. Prepare the toothpick/Q-tip/tweezers
• Examine the BASE, layout of the rollers and tape spools, the tensioning [wonder] belt, and try to figures out the intended tape path: Off the full spool, around the metal corner guide, in front of the drive wheel & metal guide, around the other corner guide, and onto the empty spool.
• The end of the tape we are interested in is most likely on the full spool (held by static cling).
• NOTE/WARNING: When you are working with the tape (rolling/ unrolling) WATCH the rollers & tensioning belt carefully. These have a tendency to work off the guides and may cause the tape to "learn to fly" after some futile attempts to put things back in place (experience speaks - that's the 1% :-)
• Turn the full spool until you can see the edge of the end of the tape and peel it off with the toothpick or tweezers. DO NOT UNROLL MORE THAN 3 INCHES! WATCH THE ROLLERS & BELT! EVERY FEW REVOLUTIONS OF THE FULL SPOOL, PRESS DOWN ALL ROLLERS TO RE-SEAT THEM!
• Holding the end of the tape with your CLEAN fingers or tweezers, wrap the tape through the tape path (see above). DO NOT YET ATTEMPT TO ROLL IT ONTO THE EMPTY REEL!
• Make sure all the rollers are firmly seated at this time. This includes BOTH spools, the drive roller, AND tensioning belt!
• Once the tape is in the tape path, unroll ONLY ENOUGH for the end to touch the empty spool.
• Using the toothpick or tweezers, press the tape end to the empty spool and gently rotate the EMPTY spool 1/4 revolution. Did the tape balloon out off the full spool or did it progress with the empty spool? If it ballooned out, don't roll it back. Instead, help it [force it] onto the empty spool with the toothpick. All you have to do is get the end of the tape under the tensioning belt. After that, the tape should go on pretty easily. If it did not balloon out but rather spooled on the empty spool, you're 80% home.
• While doing the next step, listen for "RUSTLING" sound. That sound indicates that the tape edges are getting crumpled under the tensioning belt! If you hear it, roll the tape off the empty spool and start again (if you're bold [and, I'm just itching to say, "stupid"] you can ignore the sound and there's about 60% chance that the rest of the tape will go on correctly. I do NOT recommend doing this because of the other 40%....)
• Making sure that none of the rollers are working their way up the guides, and SLOWLY and IN SMALL INCREMENTS roll the tape onto the empty spool. Turn the DRIVE wheel not the spools! (This black wheel usually has 2 indentations just for this purpose)
• You should roll on AT LEAST enough tape to get to the SECOND group of holes. You may either do this while the tape is open (easier to do it faster) or assemble the tape and do it slowly with your finger on the drive wheel.
• Pick up the plastic case and, with one finger OPEN AND KEEP OPEN the tape access door. THIS IS IMPORTANT!
• While the door is open, align the tape's BASE with the SHELL and join them GENTLY. WATCH THE TAPE!! MAKE SURE PLASTIC "fingers" ARE NOT CRUSHING THE TAPE!! If you are sure that all is well, press down harder on the shell until you hear the plastic barbs SNAP! If they do not, pick up the tape off the table and squeeze it with your fingers until they DO.
• Make sure there is no gap between the base and the shell, insert 2 screws, tighten with screwdriver. DO NOT OVER- TIGHTEN! (the plastic columns may crack or shatter)
• Sigh Loudly and Grin...

9. Lesson

After fixing, say, 3-4 tapes, this article will make much more sense. Sure, some of the procedure could be more clearly explained and you are welcome to add to this! Just e-mail any changes/corrections to me and I will add them in. Don't worry about formatting. I write in HTML which formats everything very nicely. That's how this copy was generated :-)

Note that other than some case differences, most DC6xx/6xxx series of tapes may be fixed in a similar manner. Ooh, Ahh...