No need Daniel but thanks for the offer
Its Fixed .
Yesterday I noticed the row wire on switch 21 was pretty dodgy so I resoldered it .
This morning I jumpered between row and column direct on the CPU sockets (with a diode oriented the correct way between the inputs (as per Robm's suggestion over on AA) to activate each of the 3 switches (all of which then reported closed in switch edges test) .
When I rebooted the game diagnostics passed .
So.. it seems that I did have a wiring problem and after I fixed that I should have activated each of the 3 switches .
Now to sort out why Firepower isn't booting after I swapped out the flat battery
