This is an old post, preserved for reference.
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Here's a quick preview of a couple of upcoming Commodore 64 projects.
Commodore 64 pseudo stereo dual SID
Commodore 64 PLA replacement with EPROM
Replacing the commonly faulty Commodore 64 PLA with an EPROM is something I tried a few years ago, with mixed results. I also tried to make a replacement using two GAL chips, but didn't get very far with that.