How does the positioner find track 0?!?
It's all done with that optical transduce (the glass scale, the lamp, and
a couple (or is it 3) photodetectors under the carriage). IIRC it moves
the heads towards the spindle, then as soon as it gets a valid signal
from that transducer, it locks to it and calls it
cylinder 0. Other
cylinders are then found by counting pulses from that
transducer.
Does it use the end of range microswitch and then
count? This is a bit
unclear to me.
AFAIK the microswitch is only used to disconnect the emergency-retract
battery when the heads are fully retracted. It's not part of the
positioner system, it wouldn't be repeatable enough.
BTW the drive has failed further: I powered it up, could manually load
the heads. But they are
somewhat unstable. Could not go online. The positioner force while
retracting is very low. And
Did the drive work properly after re-fitting that glass scale?
Misalignment (or mis-setup) of this will cause the head positioner to
malfunction.
I think you can disable the servo with the toggle switch on the amplifier
PCB (on top of the PSU), move the carriage _caerfully_ by hand (with a
disk loaded and spinning, of course), and look at the waveforms.
This could be a problem in just about any part of the servo analogue
electronics. The good news is that it's a pretty simple positioner servo
(no feedback form the disk itself, for example), and there shouldn't be
any prolems getting components.
everything is moving a bit. Last but not least, a PSU
regulator failed
with great optical effects.
Which one? I am wondering if you have failed power transsitors on the
servo amplifier board that are overloading one of the power rails. Ma be
worth checking.
-tony