U22 help.

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d3adpix3ls
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U22 help.

Post by d3adpix3ls »

wasn't sure what to use as a subject on this one. my c64 rev c is recovering from a failing power supply. i've switched out a couple of the ram ics, tossed in a new 5v regulator. took the time to replace a the original sockets on the SID and VIC because they were pretty corroded. it spent the past 20+ years in a barn. that's my best estimate, the guy i bought it from wasn't sure how long it had been out there. i will say that a racoon was using the box it was in as a toilet for at least a couple of months. yay! so after all of that, dead test is still flagging U22. even if i pull one of the new confirmed working ones from another socket and switch them out. got out the multi-meter and check for any damaged traces. couldn't find any. it boots to basic and will run normally for anywhere from 30 seconds to 5 minutes before the glitch gremlin returns. kinda at a loss. any input would be greatly appreciated. dying to get back to MSSIAH...


MarcWalters
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Re: U22 help.

Post by MarcWalters »

The capacitor attached to the RAM IC may be marginal due to age or damage from the erratic PSU.
d3adpix3ls
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Re: U22 help.

Post by d3adpix3ls »

just for anyone finding themselves in a similar situation. picked up a multi-pack of ceramic capacitors and just went ahead with replacing all of them. there were quite a few that looked questionable at best and would probably end up causing problems on down the road. also decided to just go ahead with pulling the remaining ram ICs. was still getting the U22 bad color ram issue with all new, know working ICs. after a good bit of digging online and through the repair manual i came to the conclusion it had to be those little multi-plex IC things. yes, pretty sure that's the technical term. i'm sticking by that. ordered a 5-pack of NOS, removed, socketed and replaced both of them just to be safe. when i tossed the deadtest cart back in, it completed a full check. no issues. she's running like a champ now. also noted that the video signal is a hell of a lot cleaner than it was previously.
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