+OLD CS1 Posted February 18, 2018 Share Posted February 18, 2018 I have two VIC-20s sitting here. One is missing its VIAs, two is not. One will give a video signal but no screen. Two gives no video signal. Moving the VIC from one to two transfers the screen behavior. I have replaced the KERNEL ROM and 6502 in both with no joy, as well as moving the 6522s around between boards. Two's 6522s are different manufacturers and vintage thus I suspect one or both have been replaced. I have been down Ray's troubleshooting guide and the thought of going after the TTL logic chips is bothersome to say the least -- this amount of work may not pay off for my purposes. Has anyone ever seen bad 6522s causing the behavior of video giving signal and black screen, with no other apparent sign of life? I have an internal source for 6522s which I can get to fairly easily. These are the two-pin power variety and the power supply is giving out 9.5VAC. I have checked the fuse and various power points around the board to confirm power is not an issue. Quote Link to comment Share on other sites More sharing options...
carlsson Posted February 18, 2018 Share Posted February 18, 2018 I can't recall if the ROM tries to initialize the 6522 and would get stuck in the process, and if that happens before the VIC chip is initialized with default values. As the 6522's are replacable, you could try to shift them on the same board to see if it makes a difference, before you get to your stash of known good VIA's. I would think something else is at fault though, some 555 timer or similar. Quote Link to comment Share on other sites More sharing options...
+OLD CS1 Posted February 18, 2018 Author Share Posted February 18, 2018 I swapped the 22s on the same board with no results. I have a 1541 with a bad drive mechanism sitting here and its 6522s in sockets. I will try those. If not I will likely just sell this off to someone who has the parts available to fix it. I was hoping to put it together with my VIC-1541 and cartridges and throw in some disk games. We shall see. Quote Link to comment Share on other sites More sharing options...
+OLD CS1 Posted February 20, 2018 Author Share Posted February 20, 2018 Welp, chip replacements and fixing cold solder joints have yielded no results. I am pretty disappointed at the quality of the soldering on this machine from the factory. In any case, I am done with this. It still does not work but with the accessories it should be worth something to someone so I am posting it up in the Marketplace. Quote Link to comment Share on other sites More sharing options...
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