Tandon TM-100-1 electronics repair

Chuck Guzis cclist at sydex.com
Thu Apr 27 14:27:28 CDT 2017

On 04/27/2017 10:42 AM, Ethan Dicks via cctalk wrote:

> It's not impossible to find another TM-100-1 or replace it with a 
> TM-100-2 (more common, owing to its appearance in the IBM 5150 PC), 
> but I'd like to just repair this one and get back to TRS-80 hacking.

The issue with Jugi's artistry is that there isn't a single version of
the PCB for the TM-100.  I have drives with 3- 4- and 6-wire steppers on
them, all taking different PCBs.

But a TM-100 is a very simple-minded device.  You can easily check its
basic mechanical operation off the system by grounding various signal
lines (all are active-low).  So you can ground the motor line to make
sure that the motor spins; you can ground the drive select to see if the
LED illuminates.  With the drive select operating, you cna use the STEP
and DIRECTION lines to move the head carriage; you can check the
operation of the track zero sensor.

Checking the read-write channel is a bit more challenging and a 'scope
can be very useful.

For lack of anything else, if you've got a PC with a floppy controller,
you can use Dave Dunfield's ImageDisk utility to perform simple checks.
He includes an RPM tester, though if the drive still has the strobe disk
attached to the spindle flywheel, a simple line-operated neon lamp can
do the same.


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