25 Apr
2005
25 Apr
'05
4:18 p.m.
I suspect the Read/Write Board. So I ordered modern
monolithic
replacements for the remaining old mono chips from Digikey, and
shotgunned all the old electrolytics etc for good measure, in two
places electrolytics replaced with tantalums (didn't have
.82uF's).
I am never in favour of shotgun replacements. It's the brother of
board-swapping in that you don't know what the fault was, you don't know
you've found it, so you can't know it's fixed.
Now, you say you _susepct_ the read/write board. Do you have a good
reason for this? You're getting random errors (so presumably it works
sometimes, you can get this drive to read/write). It might be the
read/write board. It might be the PSU. It might be the head position
servo. Etc. IMHO you need to do a lot more tests.
After warm-up, it's worse. Signals all through the
path look
COuld this be a thermal problem? Have you tried heat/freezer on chips in
the read chain and the servo?
OK, hot and cold. I can see no difference, but this is
10 MHz
NRZ data, in a two-state amp with AGC. I think I'm screwed.
Have you looked at the servo waveforms? Does this drive use the standard
optical scale transduver? What do the outputs from that look like? What
about the positioner drive signal?
-tony