PM sent re Clays guide Steevsie .

I cleaned the optos on switch 34 and switch 37 but boot up self test still fails with switch 34 fault.
I then turned off, unplugged row and column from CPU , turned back on and still self test fails with same error , but when i go into single switch test , only the 'always closed' switch is reporting closed , all others show open as I'd expect .

To recap, with the row and column plugged into the CPU its reporting all 3 through switches and the ramp up/down switch as being closed in the single switch test .

My conclusions at the moment are :-
1) U20 seems to be OK
2) I have something wrong on the playfield side
I am confused as to why self test fails with a switch error when row and column are unplugged though .

Anyone care to comment ? Suggestions ?