Hello Alessandro, I'm sending a copy of this message to the cbm-hackers list; hence I'm quoting much of your text. > I switched on and off the machine and saw that the startup message was in > red. > After some simple test I have found out that colors 4-7 in the color ram > are seen as 0-3 by the vic. > It looks like one of the data lines from the vic to the color ram is > stuck to 0. > Actually, from time to time the characters start flickering and it is > possible to see dots or lines in the correct color. > I have also seen that reading back the value in the color ram gives the > correct value. > This seems to exclude a problem in the ram itself. > To me it looks like a bad connection between the VIC and the RAM. > Do you think that the 4066 can be the reason ? > What happens if the relevant switch is always closed ? The vic will see > the normal data bus while the processor is accessing it ? Or the buffered data bus. Yes, according to the file 251027l3.gif on FUNET, the UD1 4066 (assuming that you have a VIC-20CR) is connected to VD8..VD11 and BD0..BD3. The buffer is UF8 74LS245, in the file 251027l1.gif. I don't know what failure modes are possible with the 4066, but I'd just swap that chip. > I really hope it is not the vic itself. > Do you know if someone is still selling the 6561 ? I have some 6560-101 (NTSC) chips lying around, but I don't know if anyone has spare 6561 chips. The only source for them seems to be scrapped VIC-20s. Marko Message was sent through the cbm-hackers mailing list
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