Fluke 9100 MS8425 tip

I thought I'd pass this along since I don't think it's been discussed
before. Maybe everyone but me already knew this. Hopefully it formats
properly for the TTL - sorry if the text wrapping is horrendous.

I recently had three Miniscribe 8425 drives that wouldn't format. I'd get
different errors (write errors, usually, but sometimes "drive not ready"
errors) depending on which version of the service disk I used (V1.2 versus
V1.4), and which OS software I had installed (V3.0 versus V5.0). It seems
that the drive activity LED isn't usually populated on the MS8425 (the
socket is there, but only one of my drives had the rectangular LED
installed), so I went ahead and populated all three. Hmmm, the LED flash
pattern is the same on all three drives. Hmmm, the LED flashes that pattern
even when everything except the power to the drive is disconnected (even the
WD1002S-SHD board). Aha! Some sort of drive self-test is failing on all
three drives, and it's not got anything to do with the 9100 after all!

There's not much info available out there about the MS8425, BUT there is a
little more available for the MS8438 (which is essentially the same drive),
including a spec sheet showing a list of LED flash patterns with
corresponding error descriptions. Turns out my LED pattern corresponds to
"seek error during burn-in or recal". Hmm, OK - must be a problem with the
head position sensor. It's a thru-beam flag sensor, so I dust mine off and
reseat the connector, only to get the same result. Despite the warning
label on the drives admonishing me "do not rotate interrupter", I power
things down and rotate interrupter. Power back up and BINGO! No error.
Hmm. Power down again. Power up. Still no error. Repeat for the other
drives, same result.

It seems that the MS8425 is not smart enough to find it's own home position.
That's really, really poor design. I found that the "magical" position
seems to be with the flag blocking 50% of the thru-beam sensor. I have no
idea how my three drives all got moved away from the home position
initially, but it sure seems that's what happened. I was finally able to
format the drives. Well, sort of. Two of them have "bad system sectors and
cannot be used", and the third has 1300+ bad sectors. Folks really weren't
kidding when they said the MS8425 was junk. Two small SCSI disks are on
order, so I'm sure all my problems are now solved :-)

Alex

----
ayeckley@elektronforge.com
www.elektronforge.com 
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