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This uses DC100 tapes that must be preformatted. I have a set of “new old stock” tapes still in cellophane, but it is more than likely that these tapes have completely perished by now. Despite that I would like to get the drive at least in technical good state again 
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Cleaning and repairing the cassette drives
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While it answers this nothing happens: the motor is not running at all. So, something’s wrong. The wrongness is on both drives (0 and 1), they react the same.
Getting the motor to run..
For this we need part of the schematic which can be found in the field maintenance print set for the device:
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Click the image for a large presentation.
Putting an oscilloscope on drive 1’s motor shows the following when we run the program:
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One simple step is to test the drive transistors. I desoldered the D44C8 ones (NPN) and tested them with my chinese Chinese tester; they tested OK.
Next step is to follow the signals. To help with this I run the “read” command in a loop, with a second of wait in between.
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End packet received: [success], unit 0
Read tape 1 block 40 for 8192 bytes
ERROR: Unexpected end packet: [seekError], unit 1 |
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1 |
That will be the next round of debugging…
Looking into the seek error
Both drives share the read and write logic, so we can continue with just drive 1.
Looking at the following oscilloscope image:
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Yellow: pin 6 of E28 “AMP”, the 1st exit of the amplified head signal.
Light Blue: pin 13 of E29, part of the clock detection?
Purple: pin 14 of E29, almost at the end of the RD strobe signal
Dark Blue: pin 2 of E4, RD Data H
This is the start of the run, i.e. after the motor just started reverseing.
Another run:
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This looks like it is rewinding, then reversing and trying a forward read and then giving up.
Many retries show all kinds of different errors:
ERROR: Read timeout: read 1 of 2 bytes
ERROR: Unexpected end packet: [seekError], unit 1
motorStopped
These can easily have to do with the quality of the tapes…
TU85 Tape problems
I have found a set of new old-stock tapes:
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These tapes, however, were produced in the 80’s, so they are more than 40 years old.. The tape contains a rubber band which moves the tape when the capstan wheel moves:
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This rubber band has gone bad an damaged the tape surface as can be seen here:
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This means the magnetic layer will have trouble there. It does not end there though; the magnetic layer itself has not really survived well either so it’s not that likely that we can actually read data off the tape. This is made worse by the fact that DEC TU58 tapes cannot be formatted: they came preformatted from the factory, and the TU58 firmware does not have any code in it that can format a tape. There is supposed to be firmware called tu58-i which can format- but the Internets do not seem to have it.
Let’s finish with some more images. This is a read that did several retries but ended with a seek error:
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The device does things, and there seems to be some “data”..
I’m going to assume it has been repaired, but the tapes are unreadable..
Formatting TU58 tapes
There has been some discussion about whether a TU58 can be “updated” with new firmware to format tapes. Some discussions exist where people say that there was a “tu58-i” ROM for the machine which exposed a format command.
This, however, seems unlikely to me. The tape units in the tu58 do not have any optical sensors for the BOT and EOT tape holes, i.e. these:
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In other tape drives, like the HP drives used in the 9825A/B/T and the HP-85A, there is an optical sensor which can detect these holes. The TU58 cannot. And when the tape is rewound too far it will come loose from the wheel, as the tape is not glued or hard fixed on it: the tape gets stuck to the wheel solely by being wound on it.
For me this proves that formatting tapes is impossible on a TU58.
It should, however, be possible to format them using one of the HP drives…..