14 May
2008
14 May
'08
4:12 p.m.
There's no "u" in Osborne! :-)
On Wednesday 14 May 2008 14:46, Ade Vickers wrote:
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
You mean that connector that on most of the ones I've seen have a sticker on
the front saying not to remove it while the power is on?
& the screen comes back on with the display as
steady as a rock --
Good. What I'd do there is get one of those pencil-shaped ink erasers and rub
the contacts on both sides of the board with that connector off of there,
and then put it back on, and leave it there. If you still have some erratic
operation, you can take little bits of wire-wrap wire and solder them to
both sides, which I had to do in at least one case.
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.
Monitor not getting sync would be a problem all right and if your display
problem went away that easily then maybe just cleaning those contacts up will
fix it right up.
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?
Ok, so you're getting solid video or shaky video? I thought you had said
that wiggling the connector fixed that...?
And does this unit have a screen-pac upgrade? If so, it'll have an RCA jack
in one corner of the front panel, you can feed that to a composite-input
monitor. If not we'll have to work on what's there.
I'd have a look at the outputs of the power supply, start out with the unit
off and the power disconnected and _don't_ touch that big power transistor or
it _will_ bite! Stay on the output side and measure what's there. The +5,
and + and -12 should be within 5% of where they're supposed to be,
particularly the +5. Better yet would be to scope them and see how much
trash is there. You might have power supply issues. Or you might have
monitor issues, too. I can recall reading about some monitor problems in
those machines or maybe Execs that turned out to be bad capacitors but I
can't recall which ones and I don't have those issues of Foghorn handy any
more.
I *might* have power supply schematics for that unit, I'll have to look.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin