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Atari 800 XLF Color issue


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Trying to debug another 800XL that has issues with the color circuit. Yes, it's another one - ordered this one as a spare so I had something to check against while fixing the other one, but when I got it I found that this was an 800 XLF revision 3 board instead (actually says XLF on the actual board). With an entirely different problem related to colors, what rotten luck :-(


There's some noise in the color signal and while it looks strange, the adjustment of the color pot also has a wierd effect that I'm not sure if is normal since the other one I have is not an XLF. I get vertical banding, when adjusting it seems like I'm opening colored curtains before it goes B&W (see youtube clip below, some interference with camera) instead of shifting the color spectrum. Have been trying to match this to the schematic I found by SOBOLA, but I think there are quite a few changes leading up to my revision 3 board since his revision 1.


Not sure if it matters, but I've been looking at the Phi 2 signal though it might be a totally wrong place to end up. Schematic connects phi 2 for ANTIC behind 74ls08 with GTIA getting signal directly from SALLY - the board however connect POKEY, PIA, ANTIC and GTIA via 08 pin 3 only leaving FREDDIE connected directly to SALLY pin 39. Is this normal, I could understand it if they were simply bridged but seems like completely separate on PCB so thinking schematic doesn't match up.




Edited by TEBL
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