Received a super dirty and dead Crystal Castles, with two Audio Regulator II boards.
Cleaned up the surfaces, powered on with one AR-II board. Nothing. The other AR-II board is missing caps, so we'll pass on that. Dig through the piles of stuff in the garage and come up with two AR-II boards, both test fine. Put one in, game starts up.
The game only has half the sound. I have another CC board, so I do some chip swapping and find that one of the chips at 3B/3D is bad. Between the 4 chips I have between the two boards, 3 are dead. I'll have to try and track these down. The 1P start isn't working, so I hit it with some sandpaper and it works fine now.
Some more chip testing on the other board shows a a bad 2128. The 6502 is good, but the board own't come up for some reason. Set it aside for future repair.
The trackball is SO hard to move it's not even funny. Will have to rebuild it. But it lights up properly and everything.
As it turns out, the sound chips are Atari Pokey chips. I think I'll have to search ebay for some Atari 7800 "super game cartridges" (Ballblazer, Hat Trick, Karatika, etc..), I think this is the only place you can even source them anymore.
Rebuilt the trakball, now CC is working 100%.
Things Remaining to do: