They are GI lights. So it won't be a board problem.

Just thinking out aloud - Have you upgraded to LEDS or replaced / adjusted anything recently ?

I'm thinking there is a short with a common group of GI lamps. A GI Common is shorting somewhere. Follow the GI braid and see if they are all related to the GI lamps that are out. It is going to be something simple. You just need to find it.

No, no LED's. The last thing I did was adjust a spoon switch on a pop bumper to try and get rid of a dead spot on it and It was about this time that the lights died. I figured this could have something to do with it but just can't seem to find anything which could be shorting it out.
Although the problem affects the backbox as well my gut feel is that the cause of the problem is something I've done below the playfield. Just have to find it.