Silverball is correct in that there is an led that will light when a metal ball is detected. One thing I'm a little confused with is that the powerball is not detected at all. I had the same problem but only when the ball was ejected to the shooter/plunger meaning the detected near there ball trough is the problem. If I shot the ball into the scoop area where there is a second detector the machine would know that the powerball was in play. Can you confirm whether the slot machine scoop detect recognises the powerball. If it does it then isolates it to the trough area.
BTW I soldered/hard wired the trough connectors as the prox sw 26 error started to piss me big time. Check also whether you have this error.
