22 May
2008
22 May
'08
4:56 a.m.
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.
Would appreciate any tips on troubleshooting.
Steve
--
27 May
27 May
10:29 a.m.
On Thu, 22 May 2008, 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.
Would appreciate any tips on troubleshooting.
During the recent list latency (what happened, anyway?) I tracked the
problem to a defective WD2793 FDC chip. These appear to be just about
pure unobtanium, however. Besides eBay, does anyone know of a source for
onsie-twosies?
While we're on that subject, I would love to know how to search for items
like this on Google without wading through dozens and dozens of these
obnoxious "Submit your RFQ here and we'll respond" sites. Most of them
seem rather fly-by-night, and none of them will deal in small quantities.
Steve
--
1:09 p.m.
On May 27, 2008, at 1:29 PM, Steven Hirsch wrote:
--
Dave McGuire
Port Charlotte, FL
During the recent list latency (what happened,
anyway?) I tracked
the problem to a defective WD2793 FDC chip. These appear to be
just about pure unobtanium, however. Besides eBay, does anyone
know of a source for onsie-twosies?
Unicorn Electronics (http://www.unicornelectronics.com/) has them
for eight bucks.
-Dave
3:57 p.m.
On Tue, 27 May 2008, Dave McGuire wrote:
On May 27, 2008, at 1:29 PM, Steven Hirsch wrote:
Many thanks, Dave! I thought I checked their site, but may be getting
senile. Just ordered a couple.
--
During the recent list latency (what happened,
anyway?) I tracked the
problem to a defective WD2793 FDC chip. These appear to be just about pure
unobtanium, however. Besides eBay, does anyone know of a source for
onsie-twosies?
Unicorn Electronics (http://www.unicornelectronics.com/) has them for eight
bucks. 
2:10 p.m.
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.
I don;t have the data sheet in front of me (and I certainly don't haev
the 1050 schematics here), but if that signal name 'NTRACK00' means the
obvious thing, it's _not_ Track0. In other words it should be low when
the head is on track0.
If it's not, it would explain why the drive is hammering the head into
the end stop, looking for a track 0 signal.
-tony
4 p.m.
On Tue, 27 May 2008, Tony Duell wrote:
That threw me as well. There must be a misprint somewhere, since the unit
works just fine when I substitute a known-good 2793 from another drive.
Just ordered a couple of them and hope to get this thing up and running
soon.
Steve
--
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.
I don;t have the data sheet in front of me (and I certainly don't haev
the 1050 schematics here), but if that signal name 'NTRACK00' means the
obvious thing, it's _not_ Track0. In other words it should be low when
the head is on track0.
28 May
28 May
1:15 p.m.
On Tue, 27 May 2008, Tony Duell wrote:
That threw me as well. There must be a misprint somewhere, since the unit
works just fine when I substitute a known-good 2793 from another drive.
I have checked the WD279X data sheet, and that pin is certainly
active-low. It's shown with a bar over it on the pinout diagram and in
the table of signals, it's also descried (under the 'Restore' command)
as being asserted when low.
Now, I suppose it's possible that your defective 2793 had a short from
this pin to Vcc, so that the track0 senosr circuit couldn't pull it low.
That would make it test high all the time. But if it's low normally, goes
high when the head is on track 0, and yet a new 2793 fixes the problem, I
don't know what the heck is going on.
-tony
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.
I don;t have the data sheet in front of me (and I certainly don't haev
the 1050 schematics here), but if that signal name 'NTRACK00' means the
obvious thing, it's _not_ Track0. In other words it should be low when
the head is on track0. 
27 May
27 May
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
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ard＠p850ug1.demon.co.uk -
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snhirsch＠gmail.com