At 01:18 pm 20/08/2001 +0200, you wrote: >Adrian Vickers wrote: >> Then there's the 3016 (not 4016, as I wrote in c.s.cbm). That switches on, >> and displays a picture, but it's full of garbage. > >Clear evidence of video logic which hasn't been initialized. Could be a >number of things, like a blasted ROM, faulty RAM, a broken CPU and even >the power supply. I shall try the PSU first, as that is the easiest thing to check with nothing more than a multimeter. WRT ROMs, the 3016 is the only early PET I've got; the others are both 8032-based; I'm assuming that I can't swap an awful lot with these. CPU perhaps, but the ROM surely not? Also, since the RAM is not socketed (he assumed, without looking), how can I test that - or is that the likely place for the fault if ROM/CPU/PSU are ruled out? >I once got a "slim" 4032 (which is basicly the same as a 3016 with more RAM >and upgraded ROMs, no CRTC in this case) which had exactly the same symptoms >on arrival. It worked before I shipped it. It turned out that the power >supply *was* broken. The video logic is powered independantly from the >rest of the logic. It has two 7805's, one of them powering the video, the >other one the rest. (That's not entirely true, but it does boil down to >that). In my case, the lower 7805 had died, the upper one still worked, >giving exactly the things you described. Um - so, there's a 7805 on the lower board, and a 7805 on the board inside the CRT box? Am I reading that right? > >I'd measure the supply across the processor, and see if *that* one is >at 5V too. > Will do. >> There's some photos of that one too; the display is different each time you >> power it up. > >That's because the video memory isn't initialized yet. It's containing >random data. I see. Unfortunately, I'ts been many years since I did any electronics, and I never really got above using a 555 timer... Can anyone recommend any bedside reading which would teach me the basics of IC-type elecronics (esp. microprocessor stuff)? Cheers! Ade. -- B-Racing: B where it's at :-) http://www.b-racing.co.uk Message was sent through the cbm-hackers mailing list
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