Ok I checked the driver switch matrix connectors between columns and rows and everything came up open circuit, so no shorts there.

Secondly I did the diagnostics test with the alligator lead and all the switch numbers were coming up fine until I got to pin6 on the 2J2 header.
Before then just 1 number would appear and then sequentially decrease as I moved down the header as it should indicating that particular switch number, but shorting out pin6 on the 2J2 header with any pin on the 2J3 header would give all sorts of odd numbers , but then move the alligator lead down to pin 7 on the 2J2 header and then the sequential decreasing of switch numbers would continue again all the way down to 1.

So , it would appear to be a fault with the board.
A visual inspection came up all ok, no broken tracks or shorts on the board.

So, not sure what to do next. Rottendog are closed until after the pinball show, but I guess next thing will be to email them and ask if theres anything else I can do.