Hi Philip, If you get that vertical line with the CG completely removed it is almost certainly a bit stuck low in B2, the 74LS165 shift register, or a short somewhere on the PCB around it. If you have a 5K or so resistor you could try shorting each of the pins (3,4,5,6,11,12,13,14) to ground through that; each one should add a line and the one that doesn't is presumably already grounded internally or externally somewhere. You may well also have another issue, but I'd start by checking for a short and/or replacing that chip. BTW, if you have four good spare RAM chips why not install them in I and J 7 & 8; if your ROMs are good that's all you need. Good luck! mike ----- Original Message ----- From: "Philip Lord" <email@example.com> To: <firstname.lastname@example.org> Sent: Thursday, May 12, 2011 4:30 PM Subject: Re: PET 2001 fix Part 3 - RAM/ROM board etc. > Hi guys, > It's early here (5:06am), so please excuse the brevity of my message as > I'll be going back to bed for a couple more hours after. > > I did change out the video SRAM as there were a few left over from the > main RAM that were still good. Unfortunately this did not change the > problem. Pulling the SRAM completely created a checkerboard effect, but > there were diagonal lines strafing through the pattern. I'll test this > again because at the time I didn't realize this was a valid testing > technique. > > Pulling the CG ROM takes the image back to its original state, blocks and > lines. > > One thing, late last night as I was briefly poking around with the logic > probe, there seemed to be many places where I probed that slightly > effected the pixel flicker. I didn't do much testing as it seemed a little > random and inconsistent. So maybe as Mike mentioned, it could be a power > issue. I have the board out on my desk hooked up to an original spare US > PET 2001 transformer. Maybe there is some issue with it being a US version > on 100v Japanese power. I think I have a JPN to US power step up converter > somewhere, maybe I'll try to find that. > > Thanks again > > ZZZzzz... > > > On May 13, 2011, at 4:31 AM, MikeS wrote: > >> >> ----- Original Message ----- From: "MikeS" <email@example.com> >> To: <firstname.lastname@example.org> >> Sent: Thursday, May 12, 2011 3:28 PM >> Subject: Re: PET 2001 fix Part 3 - RAM/ROM board etc. >> >> >>> Looks like the problem is mostly in the fifth character column; wonder >>> if >>> that's where the horizontal line was originally? >> >> D'oh! VERTICAL line of course... >> >> Message was sent through the cbm-hackers mailing list > > > Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing listReceived on 2011-05-13 01:00:12
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