Ok just to prove Im dumber than I look, I've spent the last 3 hours in the shed looking over this board again. Im trying to send myself insane working on a system1 board

I've got the board working again - but only when I run it from a PC power supply, It doesn't boot when using the Gottlieb power supply. Interestingly if I use the PC power supply for +5V and -12V and the gottlieb power supply for 42, 60v the machine boots fine (im making sure I have a common ground between the two power supplies).

TO make things even stranger, the PC power supply is only outputting about -11VDC, not 12V DC...

This is very strange as the Niwumpf board plays fine.

This has me wondering if I have either
1) problem with -12v rail on gottlieb power supply (Niwumpf doesn't use it)
2) enough mains noise to effect the System1 board, but not the Niwumpf
3) potentially have a startup issue with the system 1 with the games power supply not being stable when the reset goes high.

The mains noise on the Gottlieb supply is in the order of 0.05V on both 5V & -12V rail (measured with CRO). Bloody stuff all.

Im scratching my head now, can't let this go... Thinking I might throw some electrolytic caps at the Gottlieb supply.

Guess the good point is the System1 board is up and running again (well with a PC supply).

Anybody seen weird stuff like this before? Any advice...

Time to turn off the brain and go to sleep

Have you rebuilt the power supply?
The Niwumpf may be more tolerant of a crappy power supply than the original board.