28 Mar
2010
28 Mar
'10
11:23 a.m.
Hi,
I have some trouble with a 14" removable SMD disk drive (Ampex DFR 996):
When it comes to the outer tracks it starts making noises like a cat and
Based on my experiences with Pentina, I don't believe a cat makes a
unique sound...
Anyway, I assume you know it's not headcrashing (which can make a noise
like a very angry cat). I think you'd know if that was the case...
recalibrates. Endlessly. With some disks I have it
manages to crouch up
to the end, track by track with many retries. The problem seems to exist
with most of the packs I have. I played around with the head cables
while the heads are further outside. Seems to be no contact/strain
problem here. The drive seems to be working fine for the rest of the
surface. But having the end unusable makes the disks unusable for RT11
with its replacement tables. And if the drive doesn't even manage to
arrive at the end, RT11 won't even write a new directory to the disk.
The drive does not recalibrate on bad blocks. So the problem should be
in the servo system and nowhere else.
Does my problem sound familiar in any way?
Playing with the servo head amplifier gain adjustment did not help. In
fact I found out that there's a working range, and the original
adjustment was quite in the middle of that. So I kept it the way it was
adjusted. For real readjustment of the drive I'd need a disk exerciser
board, CE cartridge and some other special purpose bits. None of them
are available to me.
Another idea is that the servo data is decaying more quickly in the
center of the disk: The disk hub is held by a magnet in on the spindle.
The magnetic field and the mechanical shock while inserting the
cartridge could affect the disk. Or/and the problem could be caused by
thinner magnetic coating in the center (too close to the inner edge of
the coating?). Vague theses....
The disk drive also has a fixed disk with three disks and 5 data plus 1
servo surface. That works flawlessly.
This sounds somewhat similar in concept to the CDC 'Phoenix' drive.
There's a separate servo surface for the remvoable pack (one servo, one
data), and the 3 fixed disks (1 servo, 5 data surfaces).
What do you mean by 'outer' tracks? Normally, I would take that to mean
ones closest to the edge of the disk, but it appears you mean ones neares
the spindle.
Do you have schematics and a 'scope? The first point I would look at is
th edrive to the positioner amplifier, just to make sure there's a
component of the right frequency there to procude the noise.
Since it works correctly on the fixed disk servo surface, Iwould guess a
lot of the electronics must be working correctly. So the problem might
well be in the removable paclk's servo head, or the preamplifer stage
after it. Are there any other electronci changes made when going from the
fixed ot the removable pack (change in gain?). What about any velocity
feedback signal? That would have been an early guess of mine (lost of
this can make the servo unstable), but why would it only affect the
removeable pack?
Can you look at the output of the servo head preamplifer when using the
fixed disk (which works correctly) and the remveable disk? Step one
cylinder at a time going towards the 'bad' part and see if you can notice
any changes in the signal.
I do have a CDC Phoenix service manual, if you think the drives are
related I can take a look...
-tony