Epson PX-8 specifically TF-10 problem...

Tony Duell ard.p850ug1 at
Sun Dec 10 00:26:45 CST 2017

On Sun, Dec 10, 2017 at 2:06 AM, allison via cctalk
<cctalk at> wrote:

Assuming it's the same as the one I worked on some years ago...

>> How does it detect the presence of a disk?   and/or disk change?

It's a mechanical switch on the motor PCB. A similar switch detects
the write-protect hole.

> Functions normally save for the motor does not always turn on command
> but will if manually pushed.  All other functions are normal.
>> Totally irrelevant to the matter at hand:
>> BTW, how close to "industry standard" is the interface to the drive
>> mechanism itself?   Would it be practical to replace the mechanism
>> with one of the 80 track (and also 2 sided?) Epson drives?  Either the
>> whole drive, if it is fairly "standard", or just the stepping
>> mechanism if there is another Epson drive similar enough?
> No its an oddball.  The read-wirite electronics are part of the
> intelligent mainboard that communicates
> with the pX-8 serially.  The only board that is part of the drive is the
> motor control.

Assuming it's the same motor as the one I worked on :

What is the voltage on the collector of Q18 (== emitters of
Q15...Q17) when the motor should run but doesn't? If it's
close to the supply rail then the problem is in the motor or
commutation circuitry, if it is low then the problem is in the
speed control or the motor is not being told to run.

With the motor running, look at the waveforms on :
Collectors of Q15...Q17 (drives to the motor windings)

Pin 1,15,16 of IC13 (TA7745) (drives to those transistors)

Pins 2...7 of IC13 (outputs of the hall sensorts that detect
the motor position).

In each case the 3 (or 6) signals should look much the same,
if one is different or missing then the problem is in the motor
commutation circuit.


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