Gday all .. still looking for suggestions on this issue ..
Switch 51 and 61 not registering closed .. switch 41 has mysteriously come good (oh oh)

Also have a new more annoying fault which has made the machine unplayable !!

Right trough switch is registering open when another switch on the same column is closed (eg the other 2 trough switches or the outhole switch etc) .. this fault means you can't start a game because the CPU thinks a ball is missing . When all other switches are open in the same column this switch registers as closed (when there is a ball in that trough position), but as soon as another switch is closed in that column then this switch continuously alternates between open and closed (this is in single switch test)

I have replaced the switch because I had a spare and the original (Normally open contact) was not measuring consistently when operated.

I have also checked continutity is OK on both the row and column wires between this switch and the first switch in the row and column.

I have started to read up on fault finding WPC switch matrix issues but any help appreciated .
 

sounds to me like one of two things;

One of the switches is somehow shorted to ground intermittently. Either something silly like a lamp socket or similar is touching a lug of a switch in that row.

A switch is wired incorrectly. Also check the trough switches as there's a common between the switches that can be hanging on by a thread. Check the diodes on these switches as vibration can make them cold solder joints.