So earlier this spring I picked up an untested UniSystem board for dirt cheap. When I got it, I plugged in my CPU and PPU and tested it and found that it pretty much worked, except for one annoying glitch where when you hit the B button, it would keep repeating the action or completely ignore input from that button and affect gameplay until the machine was restarted, only to happen the next time the button was pushed.
Obviously that was unacceptable, so I put the board aside. Flash Forward to earlier this summer, where I got a Castlevania daughterboard and wanted to have a dedicated Castlevania set up. So I downloaded the UniSystem schematics, checked out the board, and found that a resistor array that somebody had changed out was the wrong one. I also found a couple spots where they had done some repairs and lifted some traces. So I ordered what I needed from Digikey.
I got the parts today, went through and changed some stuff up, socketed some chips, and redid some traces... fired it up, and boom! A perfectly working Nintendo UniSystem board. Man, I love figuring stuff out. This hobby has taught me so much.