27 May
2008
27 May
'08
6:11 p.m.
Steven Hirsch wrote:
Anyone have experience with these? I have a defective
unit (purchased
on eBay - sad story) that tries to bash the drive head to death
against the Track 0 stop when turned on. I picked up the service
manual and schematics and was able to verify that the Track 0 sensor
was working and that that NTRACK00 (pin 34) on the 2793 FDC chip is
pulled high at that point.
It looks like the head-step pulses are generated in software by the
onboard 6507 CPU. The four phases appear on PB2-5 of a 6532 IO
interface and are presumably getting cycled in the correct sequence
since the head moves quite smoothly until it hits the physical stop.
I've already verified supply voltages and inspected the board closely
for burn marks, broken traces, etc. and reseated all the socketed ICs.
The unit is fitted with the 'US Doubler' enhancement, about which I
know very little.
I don't know what the problem with your drive could be... you've already
looked
at the first thing I'd have looked at (track 0 sensor).
As for the US Doubler, I have one of those (installed it into my 1050
drive years
ago). This is a drive software change to give true double density to
the drives and
was originally used with SpartaDOS, but later I believe Dos 2.5 supports it.
It also has a high speed mode (which may only work for double density, I
don't
recall at this point).
-- Curt
Would appreciate any tips on troubleshooting.
Steve