One of the wheels has an encoder disk that has some broken parts. Is there a source to buy replacement parts for these wheels?
Not sure, but I think this
might be what you're looking for.
http://arcadefixit.com/product.sc?productId=108The site is run by KLOV's Mylstar. (Stephen Beall)
Also, one wheel only turns one direction, is that a problem with the interface board, or something else?
It could be mechanical misalignment (based on the broken teeth) but it is almost certainly not an electronic problem in the encoder board.
If it
is an electronic problem, it would be on the game PCB since both data lines have to be working to register a turn of more than one step.
No quadrature waveform transitions = no turn.
Only one data line working = wobble back and forth one step.
Scott