Thanks for all of the advise so far. I still haven't gotten to the bottom of this issue but here's where I'm upto.

Pintoxicated came around for a few games on Saturday night and game me a hand checking over Xenon.

- All GI lighting is out.
- Buzzed out the GI string and there were no signs of any loose wires. 
- GI connector at the rectifier board looks fine.
- Checked voltage at TP4 and found only around 3V (I can't remember the actual reading but it was around 3V) which should be reading 6.3V.

From here we assumed an issue with the Rectifier board, possibly a bad diode at CR1-4 so left it at that for the night thinking that I'd try a different board in it when I had so time on Sunday. Anyway I did that with the board from my Flash Gordon but it made no difference.

Any thoughts greatly appreciated.

When you say "All GI lighting is out", does that include the backbox GI or just the playfield GI?
And what about your coin lights?