WTB Miniscribe 3425 (working or parts donor)

Glen Slick glen.slick at gmail.com
Wed Nov 25 00:11:50 CST 2015

On Tue, Nov 24, 2015 at 9:45 PM, Mark J. Blair <nf6x at nf6x.net> wrote:
> Anyway, I have it happily spinning up now after moving the interruptor vane on the outer stepper motor shaft a bit. It seems that the drive expects to see the track zero sensor trip some distance before the hard stop, but not too far before. Whether the drive's idea of where track zero is vs. where it actually is on the media remains to be seen, but I'll be setting up the reader shortly. I think there may be a chance of success since, if I'm guessing correctly, track location and spacing on these drives is determined by the stepper motor, and the track zero sensor should just need to be within a half track or so of actual track zero position. Of course, all bets are off if the internal positioner roller shifted on the stepper's internal shaft, rather than just the interruptor shifting on the external shaft. Crossing my fingers...

I did some support work for a product that used a 3.5-inch 20MB
Miniscribe drive back in the mid-80's which had a failure mode where
the track zero flag would rotate slightly out of position on the
shaft. When that happened the drive would flash a specific error code
pattern on the diagnostic LED.

You could recover from that specific failure by loosening the set
screw on the flag just enough that it could be rotated without
rotating the shaft, then powering up the drive with an otherwise
unused manufacturing / test jumper pair shorted. When powered up in
that mode the LED would turn on / off just as you rotated the flag
back into the correct position in the opto sensor. When you got it
into the position where it was just at the on / off threshold you
would then carefully tighten down the set screw on the flag without
rotating the shaft. Then power cycle the drive without the test jumper
in place and hopefully all would be well.

There were specific torque limit screw drivers and a Loctite product
for the screw that were supposed to be used by the service people when
they were doing this, but that was to return the drive to service, not
just a one time data recovery. That was almost 30 years ago and I
don't remember all of the details now.

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