Another C64 to fix, help and advice needed

Make sure your 5v is OK on one of the 74 series chips around there first. Could be PLA, but the fact the RAM has different types and there was a broken trace / bad connections there could mean the RAM is the issue. I would try and get both of these up and running ;) The one with the SID issue - look at the schematics and check that each connection to the SID chip is correct. It might be missing an address or data line connection somewhere around it. On that top board, I would socket up the PLA first, test the PLA in your working system to rule it out. Then move onto the RAM perhaps. I dead test cart would be useful at this point - could help you work out whether the RAM is the problem or not. If there are the original MOS 77nn chips on there instead of 74nn chips, I would swap those out with their 74 series counterparts too - might just be one of those died.

C64 reloaded? But maybe PLA?