Now I was all set with my schematics and posho scope.
The first chip I decided to probe was the RAM connected to the CUS146.
However it was in the socket backwards, so I didn't bother. There were about 5 RAM chips in backwards on the video board.
See that bloody great big 'T' ?
Anyway, seems none of them were damaged enough to stop it working when put in properly, so I claim my bottle of wine.
edit: Lucky anyway, seeing the pinout - putting them backwards will reverse the polarity of the power pins which should theoretically exceed he -0.5V limit and trash the chips. At least there's some spares on that Final Lap PCB you could rob if they go in future.