7
David,
The small circuit board underneath the coin comparitor is called the coin-in optics.
That board is what registers coins as credits back to the MPU.
You need to take it apart and expose the coin "encoder".
The coin "encoder" guide is a plastic piece that directs the coins as they fall thru between the optical light beams called the "ABC" optics.
If the encoder is too large, a quarter can miss one of the beams and coins falling thru get "eaten"....in other words, although being directed into the hopper bowl, they don't count towards crediting the machine.
The correct "encoder" guide is one that has sort of a plastic molded bend, to push the quarter towards the left, so the coin breaks the "B" light beam of the ABC optics.
If that plastic molded guide isn't there, then you have an encoder really made for much larger casino tokens.