On Jun 7, 12:30*pm, "William Sommerwerck"
wrote:
Perished rubber belt somewhere, most likely on mode-
switch motor.
If I remember this model correcly, the mode switch is
activated by a tab that travels along the underside of one
of the cam gears. There is no "mode sw motor" involved here.
Be careful as it is easy to miss the alignment of this tab.

"Since we last spoke", I found that the capstan isn't turning. (The pinch
roller is tight against it, but the tape isn't moving.)

This is an almost-beltless transport (at least, as seen from the top). The
belt on the loading motor (?) seems to slip when it's time for the capstan
to start moving, but moves at other times.

Further thoughts?

That is very likely due to the fact that it's stretched and slick.
That particular operation of the transport demands the highest torque
and therefore that's where it slips. You can try cleaning the slick
off with 99.0% isopropyl or triclor, (if you still have any).
Sometimes giving whatever the belt is slipping on a little push along
when it starts to slip will definitely confirm this diagnosis. Try to
find a new belt just slightly smaller, (but same thickness) than the
one presently on the machine to account for the increase in diameter.
PRB used to be a good supplier of belts. Don't know if they're still
around. Those were good machines. It would be a shame to let it go for
a relatively simple problem. Lenny