24 Apr
2005
24 Apr
'05
4:55 p.m.
I've been working on my car project
(http://wps.com/AMC/1970-AMC-Hornet/index.html) because car season
is coming up soon enough, but I peeled time out for the Nova here
and there.
I originally repaired a popped +5V logic bypass cap on the
Read/Write Board, (some monolithic ceramic job), and changed all
the funky old caps for new ceramic disks. That worked for 20 - 40
hours of operation without a single error. Disk had formatted with
zero media defects. Then the disk started throwing read errors
that moved around (bad blocks later good; more and more bad
blocks...). Diagnostics never indicated any error other than read
errors; seek, format, diags all run 100% perfect except read
errors.
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).
Install board with all new chips and alcohol wash, format -- hard
100% read failure! D'OH! Long story short, I found internal +6V
was not; turns out I installed a tant backwards. doh. New tant,
+6V fine.
Formats, reads OK, then errors again! Sheesh! System has been on
for two hours (I'm getting paranoid, so temp stabilize the whole
thing); halted diags, loaded disk heads, installed drive cover,
pushed into the rack, left for an hour for the drive temp to
stabilize (this is a religious rite, might as well kill a chicken)
then format and test again.
After warm-up, it's worse. Signals all through the path look
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.
The R/W board is a piece of work too. I suspect it's an early
revision, as the board is a hack job, covered in cut traces,
components and jumpers on the bottom, and there's a !#$%!! trimpot
crammed in somewhere as well as kludgey RC (lopass) networks in
some digital logic. Plus, the PC board was milled out for access
to a middle layer. Not Good. Plus, it doesn't match the schematic
(though it's close enough to poke around in with a scope).
Photos of the nasty board here,
http://wps.com/NOVA4/pitchas.html
About halfway down.
Anyone got a spare board?!
24 Apr
24 Apr
5:19 p.m.
On Sun, 24 Apr 2005, Tom Jennings wrote:
After warm-up, it's worse. Signals all through the path look
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.
Um, scrub the heads real good again? Murphy may have been a lot of
things, but subtle wasn't one of them....
Cheers
John
5:58 p.m.
At 04:55 PM 4/24/05 -0700, you wrote:
I've been working on my car project
(http://wps.com/AMC/1970-AMC-Hornet/index.html) because car season
is coming up soon enough, but I peeled time out for the Nova here
and there.
I originally repaired a popped +5V logic bypass cap on the
Read/Write Board, (some monolithic ceramic job), and changed all
the funky old caps for new ceramic disks. That worked for 20 - 40
hours of operation without a single error. Disk had formatted with
zero media defects. Then the disk started throwing read errors
that moved around (bad blocks later good; more and more bad
blocks...). Diagnostics never indicated any error other than read
errors; seek, format, diags all run 100% perfect except read
errors.
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).
Install board with all new chips and alcohol wash, format -- hard
100% read failure! D'OH! Long story short, I found internal +6V
was not; turns out I installed a tant backwards. doh. New tant,
+6V fine.
Formats, reads OK, then errors again! Sheesh! System has been on
for two hours (I'm getting paranoid, so temp stabilize the whole
thing); halted diags, loaded disk heads, installed drive cover,
pushed into the rack, left for an hour for the drive temp to
stabilize (this is a religious rite, might as well kill a chicken)
then format and test again.
After warm-up, it's worse. Signals all through the path look
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.
The R/W board is a piece of work too. I suspect it's an early
revision, as the board is a hack job, covered in cut traces,
components and jumpers on the bottom, and there's a !#$%!! trimpot
crammed in somewhere as well as kludgey RC (lopass) networks in
some digital logic. Plus, the PC board was milled out for access
to a middle layer. Not Good. Plus, it doesn't match the schematic
(though it's close enough to poke around in with a scope).
Photos of the nasty board here,
http://wps.com/NOVA4/pitchas.html
How come it says "forbidden" when I try to get a close up view of the
picture?
About halfway down.
Anyone got a spare board?!
Maybe! There's a pair of Nova 4s in a local scrap yard. One looks
complete and the other gutted. Exactly where is the board located in the
unit? Where are you located?
Joe
10:03 p.m.
On Sun, 24 Apr 2005, Joe R. wrote:
My bad, permissions fixed.
Photos of the
nasty board here,
http://wps.com/NOVA4/pitchas.html
How come it says "forbidden" when I try to get a close up view of the
picture?
10:07 p.m.
On Sun, 24 Apr 2005, Joe R. wrote:
Maybe! There's a pair of Nova 4s in a local scrap
yard. One looks
complete and the other gutted. Exactly where is the board located in the
unit? Where are you located?
Take them all!! There aren't that many Novas around, please yank
all/any cards from the CPU chassis. They can be ID'd by number.
The disk boards are in the ... disk drive. There are many
different drives of course. THe R/W board is small and bolted to
the chassis, to the right of the head assembly.
Removable platter, heads, cards, etc all welcome...
25 Apr
25 Apr
6:23 a.m.
At 10:07 PM 4/24/05 -0700, you wrote:
On Sun, 24 Apr 2005, Joe R. wrote:
Why did I know THAT was coming :-)
OK I'll see what I can do. The owner there is funny about this stuff.
If he thinks there's gold anywhere in it, forget it!
Joe
Maybe! There's a pair of Nova 4s in a local
scrap yard. One looks
complete and the other gutted. Exactly where is the board located in the
unit? Where are you located?
Take them all!! There aren't that many Novas around, please yank
all/any cards from the CPU chassis. They can be ID'd by number.
The disk boards are in the ... disk drive. There are many
different drives of course. THe R/W board is small and bolted to
the chassis, to the right of the head assembly.
Removable platter, heads, cards, etc all welcome...
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
5:26 p.m.
Tony wrote:
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.
I'm not a fan of shotgun replacements. Board-swapping can be a useful
diagnostic measure, in that if you swap a board out and the machine
starts working, you have most likely isolated the fault to that board,
making it easier to focus your efforts to track down the actual failed
component.
I've found this technique to be especially useful when the symptom is
sporadic flakyness.
Of course, if you're not careful, it's possible that there was some
fault that damaged that board and will damage the one you swap into
its place. At the very least the power supply voltages should be
checked before board swapping.
Eric
6:09 p.m.
Tony wrote:
With the emphasiss on 'likely'...
I have actually seen a case like that (somewhat simplified) :
2 modules, A and B. Module A outputs a signal to B. A was marginal, but
withing spec on timing, B was just out of spec. System failed. Replacing
_A_ with one that was less marginal got the system to work. So you spend
a long time working on the old module A, which in fact is working within
spec, missing the fact that B is the problem.
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.
I'm not a fan of shotgun replacements. Board-swapping can be a useful
diagnostic measure, in that if you swap a board out and the machine
starts working, you have most likely isolated the fault to that board, making it easier to focus your efforts to track down
the actual failed
component.
I've found this technique to be especially useful when the symptom is
sporadic flakyness.
And that's the one time I'd never use it. Intermittant faults are a pain
to trace because you don't know you've fixed them (Murphey's law will
ensure tha the machine works fro a bit after you've done something to it
:-)). With such faults you _must_ find the real cause and put it right.
Swap modules, you might think you've traced the fault to a particular
module, only for it to come back and bite you later on because it was
somewhere totally different.
-tony
7180
days inactive
7182
days old
8 comments
5 participants
participants (5)
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ard＠p850ug1.demon.co.uk -
eric＠brouhaha.com -
jpl15＠panix.com -
rigdonj＠cfl.rr.com -
tomj＠wps.com