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I have 6540-019 in my PET 2001-8C, apparently there might be a -011 instead. As far as I can determine they differ in 15 bytes, in this area: -011 version: .C:c584 A2 68 LDX #$68 .C:c586 86 65 STX $65 .C:c588 68 PLA .C:c589 8D FD 01 STA $01FD .C:c58c 68...

No, swapping 6522 didn't make any difference. It's possible there's a problem with the socket maybe, I can check continuity unless you have other ideas? I tried swapping the 6502 as well since it was socketed in the VIC as well - as expected, no change. I'm wondering if my temporary eprom...

Now measuring the proper pins (with logic probe) with the GND cable steadily attached this time. They're both the same signal but the pulse train from pin5 is about 1.3ms (half a pulse width) after, 60Hz negative pulse, pulse width about 2.56ms. So in 1.28ms divisions logic looks like this...

I tried the POKE59458,62, it was hard to notice any difference in game but I got new occasional interference at the prompt asking to play again, almost a character long showing here and there. I have tried swapping video ram for a new pair before (same as plain ram), didn't notice any...

... and also upon pressing enter when entering a line of program in BASIC. Looks like this when running Fire! https://www.youtube.com/watch?v=Ey8gmapT_3I It's small horizontal lines in a diagonal kind of pattern, appears on every screen update in the clip as far as I can see, quite...

I successfully tested all 6540 ROM with the Willem eprom programmer, a breadboard, 74LS14, machined socket and a lot of breadboard wires... Turns out one was bad, got glitches here and there when reading, it never verified correctly. So, thinking if there's a neat way to test the 6550 RAM...