12 Aug
2013
12 Aug
'13
12:16 p.m.
The problem indeed is often caused by a gummy part going to goo after
some years...
The head assembly can move around a fixed axis near a front edge of the
disk.
The extremes of this movement have a couple of bumpers of this
short-lasting gummy,
that after 10 years goes to a viscous black material, loosing its tickness:
that is, the extremes of the movement are now some degree more than the
original device.
Note that the bumpers are attached to metal holders that can be moved
sligtly and that are fixed to
the holding structure with two bolts each. (i can provide pictures of it
all).
The heads when the disk is stopped down "fly" to the park position, that
is on one of the extreme
(the most inner position over the disks).
As the disk is powered up, the electronics put the heads to the inner
end of the parking area,
so the mechanical lock, that holds the heads even when the disk is
powered down, can be easily disengaged.
On the faulty drives, because of the loss of thickness of the bumpers,
this operation let the head to fall
outside the park area (too much toward the inner part of the disk)
causing the electronics to detect a problems,
and so forcing a new park operation, and all restarts....
I fixed this problem on a couple of disks.
I needed to open the disks in a very clean room (few dust around),
powering the disk at open-hearth,
loosing a little the two bolts of the park area extreme, and moving the
bumper holder slowly with the disk in
movement, so letting it retry the spin-up sequence, until it seems to
regain normal operation.
Then I give a little bit more of thickness (we are talking about 0.1mm
more or so) and refixed the two bolts.
Then I tried to power-down and power-up to be sure that all works well.
This saved a couple of disks completely.
If you need it, I can supply good pictures of the inside of the disk,
with some more advice.
Andrea
13 Aug
13 Aug
12:51 a.m.
On Aug 12, 2013, at 12:16 PM, shadoooo wrote:
On the faulty drives, because of the loss of thickness
of the bumpers, this operation let the head to fall outside the park area (too much toward
the inner part of the disk) causing the electronics to detect a problems, and so forcing a
new park operation, and all restarts....
Well, chap my hide. I've accumulated a pile of 1325s (some with data I badly wanted to
recover) that came to me with the sticky bumpers problem, but only managed to get a 20% or
so success rate reviving them after cleaning the goo out. I was starting to get
depressed.
Somehow I never saw the original message on the list (did it only go to cctalk?)
discussing how the thickness of the bumper matters (after observing it closer, now, I can
easily see how). So, THANK YOU VERY MUCH for bringing it up again, because the #1 drive I
most wanted to revive is now working again, simply after adjusting the stop. I suspect the
rest will magically come to life again too.
I'm chuffed, hey?
...on a different but related topic, anybody have any similar, magic resurrection tricks
for Quantum Q250/Q280 5.25" HH SCSI drives, like used on the original Mac II and IIx?
I have a pile that are all failing in suspiciously similar ways, that make me think
it's something relatively simple to repair (if only I could determine what). I'd
suspect capacitors, but they all appear to be tantalum and thus unlikely to have failed
(at least, in any subtle way). I may try replacing them anyway, just to see what happens.
This latest Q280 is dying in a new way, that seems possibly related if I squint just
right. It's getting 'distracted'. It works and reads fine, but sometimes takes
minutes to actually respond. The activity light will be lit solid the whole time. Just an
hour ago I discovered that if you jostle it ever so slightly while it's
'distracted', it 'wakes up' and does the read or write normally.
Formatting it makes it work normally for a few days. Makes me think there's some kind
of very, very slight positioning error happening, that gets worse over time, possibly
ultimately ending up like most of my Q250s, which fail to format, but on different sets of
blocks every time, which then fail to be relocated. Positioning error? Read amplifier? If
somebody's been down this road already I'd be happy to take advice.
ok
bear.
--
until further notice
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bear＠typewritten.org -
shadoooo＠gmail.com