More than anything I think the game is living up to it's name.
And just to be sure, you are testing the trough proximity? When you state you put the balls "near" the board, are you cycling them through the trough as they would cycle normally? If yes, then you might have a bug in the software/firmware, go ahead and change the powerball setting in the program (yes I know it's correct right now) for a few games and then change it back. If you want to get extreme then remove the batteries (word of caution you will loose all programing and high scores). The other thing, although the hardware works in test mode doesn't mean it's 100% working in game mode. If it is weak (connector/sensor) then I've seen them work in test but not game. The clock opto's are a good example, I had one that the opto's were fine in test but in game one was intermitten and thus the clock would shut down. Believe me, that proximity sensor can be a real bugger.
