14 May
2008
14 May
'08
12:23 p.m.
Ade,
I don't know the internals of the Osborne but can help you with some repair
rules of thump .
First step, is checking the boards visual for corosion and bad solder joints
(crystaline with a round marking in the solder) good joints are shiny and
curved, if you don't trust one remove the old solder and resolder.
And of cause scheck the board for burned and broken components
Second step, is to locate the power supply and check the voltages with a
multimeter, after that you check them with the scope for ripple and spikes.
Typical PSU should have no more then 100-300mV ripple spikes and noise.
If there is a lot of noise or spikes check the decoupling Elco's and
tantalium C's if you have a lot of ripple that indicates a bad ripple elco
in the PSU.
Sometimes placing a few 200nF C's over the +5V rejects a lot of noise and
will give you a good indication were to look (decoupling C's)
Third, check components for heat development, heated components indicates
shortcuts.
When old electronics is stowed away in storages for a long time, elcos are
going to degrade and eventualy won't work at all.
The picture your showing indicates a fault in the horizontal sync circuit
of the video, pausible cause degraded elco's.
This also can be the cause at a bad startup due to a short reset time, witch
would be caused by a elco with a too low capacity.
Rik
----- Original Message -----
From: "Ade Vickers" <javickers at solutionengineers.com>
To: "CCTalk" <cctalk at classiccmp.org>
Sent: Wednesday, May 14, 2008 8:46 PM
Subject: Osbourne OCC1 problem
Hi folks,
I just dug my old Osborne OCC1 (1st model, in the beige vacuum-formed ABS
case), only to find all is not well. Actually, "finding" all is not well
is
a bit of a white lie - I already knew it was in trouble, from when I last
tried to boot it about 2 years ago...
Unfortunately, the intervening 2 years have failed to fix the problem,
which
is that the video seems to have no horizontal hold.
It took a few goes, but eventually it booted from a CP/M disk; with
scrambled video. The links below are to a picture & two versions of the
same
video (16 seconds of special-effects laden trickery...):
PIC: The startup screen in scrambled fashion:
http://www.solutionengineer.com/ozzie/occ1_prb.jpg
VID: Booting to CP/M:
MOV format (4mb): http://www.solutionengineer.com/ozzie/occ1_prb.mov
MPEG2 format (9mb):
http://www.solutionengineer.com/ozzie/occ1_prb.mpg
Please excuse the camera wobble on the movie... The constant high-pitch
whine is, I think, the image stabiliser in my camera working away.
Now.... If I pull the termination block off the External Video connector,
the screen goes out (as one would expect); push it back on & the screen
comes back on with the display as steady as a rock -- unfortunately, it's
crashed the computer... From this, I deduce that it must be something in
the
mainboard electronics that's failed (a cap, maybe?), rather than something
in the monitor unit.
Any ideas where to start looking? I have an oscilloscope (albeit I've
forgotten how to use it, and am not 100% sure where the probes are), and a
multimeter... beyond that, not a lot.
I've tried cleaning the contacts to the monitor, and around the Ext Vid.
termination block; and I've wiggled the three cable connectors to the
mainboard a few times to clean them up. I've also popped each of the three
socketed chips in & out a couple of time to clean the legs up. Finally, I
soldered the contrast knob back together - one of the legs had broken.
Basically, everything works except for the shaky video. Sometimes you see
a
whole page full of 1s, or 0s; essentially, it's all a bit random. Bad
connection somewhere, perhaps, or maybe a failing chip?
Cheers!
Ade.
No virus found in this outgoing message.
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Version: 7.5.524 / Virus Database: 269.23.16/1431 - Release Date:
13/05/2008
19:55
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7:49
