It should be
fairly easy to check the widnig nfor continuity and to look
at the hall sensor output while turnig nthe motor by hand with power applied.
I
think the winding is intact, as it will move with power applied. I
would think it would do nothing with a break in the winding. hall
sensor is easy to test as well.
Rememebr that it's a centre-tapepd winding with the tap goign to +12V via
the motor-on swtichign circuit. If one half of the widnign aaswas open,
it might still move a little when powered up.
If the hall switch has died you have problems. It's inside the motor.
AFAIK there si no way to get to it without (a) dismantlign the compelte
HDA) and (b) using a hydraulic prsss to get the motor apart. But most
liklely the problem ias a pwoer transistor failure.
Incidentally, 'my' scheamtics for the HP9133H (not the V/XV whcih is
totally different) on
http://www.hpmuseum.net/ include the ST225.
-tony