7900A drive: 1 , Me - 0

From: Joe <rigdonj_at_intellistar.net>
Date: Wed Sep 8 01:42:44 1999

Jay,

   This is just a shot in the dark but I used to work on large voice coil
drives and they used a Saft NiCad battery to retract the heads. The %$^%&^%
Saft batteries were no good and we often lost disks and heads due to them
not retracting. In theory, the battery was there to supply power and
retract the heads in case the drive lost AC power but they cut corners and
also used it retract the heads even when AC power was still available. So
much for theory! Look around carefully and see if it might have a battery
or possible even a large capacitor in it and check it carefully.

  Joe

At 10:15 PM 9/7/99 -0500, you wrote:
>Here's another installment in the ongoing HP7900A drive saga (yes, it's a
>plea for advice and/or sympathy <grin>)
>
>Installed new (refurbed) lower heads and new lower platter. Recleaned inside
>of drive. Powered up, put in new removable cartridge. Hit load switch and
>waited 25 seconds, then hit unload. Did this a few times (the blowers and
>drive spins up, but the heads don't load for 30 seconds - did this to get
>any remaining particles out). Removed cartridge, powered down, removed
>covers and reinspected everything inside. All looked well (including heads,
>which were fully retracted).
>
>So, this time I powered up and hit load. Waited 30 seconds, heard the heads
>move out to cylinder 0. Ran drive like this for about 3 minutes, no problem.
>Hit unload. When I removed the removable cartridge, I noticed the heads
>weren't quite retracted all the way. They were well off the media, but not
>all the way back home (the heads weren't touching each other, but they were
>close). Manually pushed the heads back, rechecked everything I could find.
>Repowered up the drive, after 30 seconds the heads loaded. Drive ready lite
>comes on and ran for about 15 minutes. No HDI sounds at all. I was elated.
>Hit unload, and after about 20 seconds heard very soft HDI. This time I left
>the cartridge in, powered everything off, removed the covers, and this time
>the heads weren't retracted at all. They were sitting right on the media.
>Strange thing is, there's no marks on the media, the lower heads I replaced
>look pristine, and the upper heads have only the very slightest indication
>of oxide.
>
>Gee - perhaps this is why the drive originally had a head crash before I got
>it? I've been through the "theory of operation" text and flowcharts. Several
>things confuse me. First, I thought that hitting the unload switch was
>pretty much of an immediate voice coil retraction - I didn't think this went
>through all the normal logic circuits. Second, the coil can't be completely
>shot I wouldn't think, because as I understand it the drive ready light
>won't even come on unless the positioner moves out to cyl 0 correctly.
>Before I replaced the heads and media, I don't THINK I had this problem, I
>think I would have noticed if the heads weren't retracting before. But, I
>can't imagine that anything I did related to replacing the lower head set
>and the lower platter would have anything to do with this. Input anyone?????
>
>TIA!
>
>Jay West
>
>
Received on Wed Sep 08 1999 - 01:42:44 BST