Is this your first Gottlieb? They are a different beast. Not saying that is a bad thing - just different. I have seen some strange issues on System 80 stuff. My first guess is what is already been mentioned (diode or switch issues). The cable that runs between the MPU and driver board is critical. Bad pins will cause all sorts of issues. Most of the Gottlieb grounding issues are caused by weak / bad pins. I also seem to remember Black Hole not being 100% LED capable. I would have got it 100% functional before changing over to LEDs. Baby steps are needed when install LEDs on these. That way you can correct issues caused by LEDs as you go.