I checked the slam switches and they looked ok.
I played a game with the glass of and flicked the slam switches a few times and it seemed to play ok.
Wondering if the switches had a bit of crud on them or something and flicking them around gave a good contact.
I might even disable the slam by jumpering the mpu as shown on the marvin guide.
thanks for the help guys.
I'd simply jumper them. The game is a home use machine now !