OK yes, Pin 3??
Pin 10 is +12.
Tested again, so pin 10 (U20) good 12v same as U18 & U19. They all buzz out together so must share the same rail.
Jumpered PIN10 U20 to pin 3 U16.
All good.
Just letting run for a while to ensure no phantoms and will test all playfield switches again.
I suspect the cleaning and movement in / out may have caused issues where the batt damage had been. I am still going to put a Rottendog board in. I think this will be a better option for the long term.
Thanks MM,
PS. Even after you explained everything I cannot read that schematic. I will keep trying though..