Tandon TM100-2A Logic Board Failure

[Formulator]

I recently purchased (2) TM100's from a local dealer $5 apiece. One from '83, one from '86. They were advertised as "non-operational."

However, after replacing the logic boards with ones from working drives it shows the heads and servo boards are working. I used one for a Kaypro that had a broken door latch.

So, when a logic board fails, what may be the likely cause? There are no bent posts and the boards appear to have no visible damage. I can provide images if needed.

Thanks.

 

[SomeGuy]

I don't believe there is any kind of common failure, although I personally would be a hair more suspicious of chips connected directly to the card edge connector.

But you can narrow the issue down by testing various drive operations. Just off the top of my head:
does the drive become selected?
does the motor spin when it is supposed to?
does the head step in and out?
does the head return to track zero and stop?
can it read a track from an existing disk?
can it write a track?
does the index line pulse as the disk spins?

Since an alternate logic board works, we can assume head alignment is OK, and drive RPM (controlled by the smaller motor board) is OK.

 

[Chuck(G)]

If the faulty board refuses to seek, I've seen failures with the stepper driver ICs before. There's a Sams Photofact for the TM-100 wandering around (MZD?); it'll help you troubleshoot.

 

[modem7]

There are no bent posts and the boards appear to have no visible damage.

Did that include a good look at inductor L4. See [here].