TU10 tape drive restoration

djg at pdp8.net djg at pdp8.net
Sun Feb 17 13:02:13 CST 2008

I am working on restoring a DEC TU10 tape drive for my PDP-8/E and want to 
see if anybody has experience repairing them before I do too much to it. 
It was made in 1973 and probably last powered up in 1988. I have the 
maintenance manuals and prints for it. Though for some reason they don't 
have the 20 year idle maintenance procedure.

Does anybody have a TU10 with a good capstan who can accurately measure
the diameter or the coating thickness?

Also does anybody have a 9 track 800 BPI alignment/skew tape? A bunch
of the maintenance procedures use it.

So far I have cleaned it and taken stock of its condition.
   The vacuum switches are bad but it looks like they are still made 
by World Magnetics so I should be able to get new. The markings on them 
don't exactly match the new parts so hopefully the manual 10" H2O 
is correct. If anybody knows more it would be appreciated.
   The capstan is past dead and seriously into decomposing. The price for a
NOS one is scary. It is about 1.8" in diameter and directly moves the
tape. Since this is a critical component to the tape path I suspect my skills 
with the do it yourself repairs will leave it too lopsided. Has anybody
tried www.terrysrubberrollers.com. I saw a couple references on the list but
didn't see any reports of results. It looks like he uses some black rubber
which I don't know if it will have similar friction to the original.
>From whats left it looks like the original capstan was translucent amber.
   The blower sound noisy when turned by hand.  Plan to see if I can
open and inspect.
   One of the reels doesn't turn easily.  The manual has a section on
cleaning the brakes so plan to do that.
   Plan to do the standard power supply checkout.

A lot of the old equipment like this tape drive has parts with permanently 
lubricated ball bearings. So far I have decides that if the device sounds 
fine to leave them alone since it won't get that much use and taking it
apart enough to get the bearings out has some risk. They also are sometimes
pretty well sealed making cleaning and relubricated difficult.  I have 
wondered how good 20-30 year old grease can be. What do other people do?
Has anybody found a good way to relubricate these type of bearings to 
prolong the life? Or wait until they fail and hope the bearing assembly 
matches something you can buy?

David Gesswein
http://www.pdp8online.com/ -- Run an old computer with blinkenlights

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