[sci.electronics] hard disk stumpper, part II

piner@newton.physics.purdue.edu (Richard Piner) (08/24/90)

Thanks for all the suggestions on fixing my hard disk subsystem.
It turns out everyone was wrong, including me. It is possible to have
two disk drives go bad. 
I after checking the signals passed back and forth between disk and
controller, I was sure the problem was not in the cables. By the way,
some folks thought this might be a system I was putting together. It
was not. It was a system that had been working just fine when placed
in storage three years ago. I had left the system running the whole three
years, and had checked on it every few weeks. But I had never tried to
write to the disk during that time. Anyway, to find out why the disks would not
format, I hacked in some error message printouts into the hard disk
formatting software. (Always get source code when you buy!) While doing
this, I found serious bugs in the software. It turns out, the software would
only work correctly, if there were no problems during a format/verify.
If there were any errors during the formating or verifying of the disk,
the software would screw up. After fixing all of this, I found that
one drive was giving "write faults" on all tracks. A check with the scope
confirmed this. The second drive, which had been sitting in a box since
1984, gave soft errors during verify on one track, which now the software
CORRECTLY locks out. So now I have a working drive.
The first drive has a burned out fuse on the PC board. I assume that
this is why the "write fault" signal is set. I would like to get this drive
working since it is the newer of the two drives. But, this fuse is an odd
one. It is 7 tiny fuses in a 14 pin dip package. I've never seen anything
like it. It has no part number, but is marked "AMP". I've looked in
the Newark catalog and found nothing like it. I'll try to call Miniscribe
tomorrow and find out what the part number is and a distibutor for this
odd fuse. Thanks again to everyone, and I thought you all might like to
know how this puzzle workek out. The extra Xebec controller I got from
Computer Surplus Store seems to be working ok.

						R. Piner