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From: jrefling@rosslare.ece.uci.edu (John Refling)
Newsgroups: comp.sys.dec
Subject: ONE REASON why RD53's spin up and then shutdown (visually verified)
Date: 16 Jun 1994 18:17:22 GMT
Organization: University of California, Irvine
Lines: 40
Message-ID: <2tq4vi$p5@news.service.uci.edu>
NNTP-Posting-Host: rosslare.ece.uci.edu
Keywords: RD53


Well, there has been lots of speculation on this topic, so I will add my
observations.  First, we have all heard about the possibilites of bearing
friction, friction from the grounding strap, microscopic breaks in the
clear strip cabling, changing tolerances in the sense amplifiers, etc.

With some dead drives and some working drives, I decided to get to the
bottom of this once and for all.  After swapping ALL the circuit boards
(including some nicely hidden under aluminum panels) and testing all the
clear flexible ribbon cables, I concluded that the problem was not
electrical.  So, is it the bearings?  Who knows.  Nothing in the motor
control section got hot, so nothing was being overloaded.  With a
tachometer, one could check the speed, but I didn't have one.

But I had heard a rumor elsewhere:  that the head positioner would
get stuck.  I looked at the inside of a failed drive, and sure enough,
there is a little rubber bumper at each end of the head positioner's
play.  This over the years, had turned to goo, and apparently the
positioner was not powerful enough to overcome this.  I have seen this
happen to lots of things (laser printers, instruments on my car, etc).

Well I was able to swap my bad drives for good drives so I couldn't
try the drive out again after unsticking the head positioner to
electrically verify this observation.  BUT I have heard from drive
repair depots that this is indeed the failure mode of these drives.
Apparently, when the sense amplifiers don't get the track signals
within a certain amount of time, the motor is shut down.

There are at least three possibilities to fix this: 1) open the drive up
in a clean room (or a relatively dust free place if you just want to
run the thing long enough to backup data) and unstick the positioner.
2) put it flat on a table and hit the case from the side with a hammer
to unstick the head positioner.  3) put a current surge through the
head positioner electromagnet.  I haven't tried any of these.

(or possibily 4: swap the drives with working ones that no one wants).

All pose danger to the data, and I wouldn't try any unless the drive is
about to go into the trash.  Needless to say, I take no responsibility
for any of this --- you're on your own!