I have an S+ Pinball machine (16Mhz MPU) which has always worked perfectly, but it is now developing an intermittent sound problem. The regular game sound works fine but occasionally when it goes into the bonus mode it is silent. The last time it went silent in bonus mode, I immediately opened and closed the door, then it resumed and the sound was back.
I haven't a clue where to begin looking for the problem. Hoping for some input. Keep in mind that the regular game sound has never had a glitch. It only happens during the bonus round (same speaker).