I think you have a switch issue - it sounds like the Advance button is being read as closed. I had a similar problem and tracked it down to a broken diode on one of the coin switches. I'd check all of the switches in the same row and column as the test switches.

It's also possible that the chip that implements the switch matrix is bad (I forgot which one this is). You could check that with a logic probe; a DMM isn't much help there.