7900A drive: 1 , Me - 1/2

From: Jay West <jlwest_at_tseinc.com>
Date: Wed Sep 8 19:56:30 1999

The score narrows, but I can't claim a complete victory....

Tony wrote...
>Well, if the servo can lock the heads in both directions, then the power
>rails are probably OK (although it can't hurt to check them). Your next
>job (and I can't help here as I don't have the schematics) is to figure
>out how it unloads the heads (where does it apply the unload signal, what
>causes it, etc) and then to check through the electronics. It's not that

I went through the schematics, concentrating on the PMR board (Power
regulator) and Drive control board. Not in great detail, but just enough to
get a general gist of the sequence of events and "who does what". I then
went down and checked the disc power supply (it's a separate rackmount
unit). Then before starting to follow traces and wires I decided to pull all
the connections from the rest of the system to the PMR board. I was
specifically looking for wires that had come loose, or pins that weren't
pushed all the way in the connector, etc. Double checked that my hand
written labels on the connectors (done before removing them) showed that all
the connectors were back in the right place.

Powered the drive up - heads seeked and drive ready came on. Hit the unload
switch, and the heads immediately retracted and the brake engaged. Did this
about 10 times in a row, every time the heads retracted nicely just like
they're supposed to. Hummm... this leads me to one of two possible
conclusions: A) there was just a loose connector, or B) this is a total
co-incidence that it started working and the problem might very easily
happen again. Now that it's working, further troubleshooting to be sure of
the exact cause is not easy. I Know I had all the connectors pushed down
firm and in the correct place before, but, it does work now (at least 10
times anyway, my luck the 11th time would have been the failure).

Followup questions:
1) The drive innards are dusty again, must be the environment (or running
with the covers removed didn't help I guess). What is the best way to get
all the dust out? Canned air doesn't begin to get the dust off the plastic
surfaces, neither does a DP-style vacuum. Any tips/tricks anyone would care
to pass on?

2) From the previous spin-down with the heads on the platter, the bottom
heads are mint but the top heads now have oxide streaks on them. Cleaning
with foam qtips and IPA doesn't budge any of it. I am loath to take out the
top heads (removable platter) and send them out for recontouring and
test-fly because then the drive will need to be re-aligned and I don't have
an alignment cartridge (and probably the know-how) to realign them. This is
only important because I have a diagnostic cartridge that I need to be able
to read for additional cpu/disk/tape diagnostics on down the road. Is it the
general consensus that heads in this condition are ok to use or am I setting
myself up for a major problem. What I'm hoping is on down the road to get
the diagnostics copied from cartridge to 1/2 tape. Then I can send the heads
off and not bother with re-alignment (other than having to reformat my
cartridges and lay data from tape back down. Bad idea?


Jay West
Received on Wed Sep 08 1999 - 19:56:30 BST

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