Osbourne OCC1 problem

From: Ade Vickers <javickers at solutionengineers.com> Subject: Osbourne OCC1 problem To: "CCTalk" <cctalk at classiccmp.org> Date: Wednesday, May 14, 2008, 11:46 AM 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. Checked by AVG. Version: 7.5.524 / Virus Database: 269.23.16/1431 - Release Date: 13/05/2008 19:55