update on the bell opto board. the customer received the new opto board, the customer fitted it and it lasted one game and it died again only this time only the bell wouldn't work and no other switches were locked on.

so another one was sent and i fitted it after checking the machine over for any shorts or problems in the switch matrix and no sign of any problems.  

I have ordered some replacement mosfets for the opto board to replace the 2 faulty ones. so the customer will have a couple of spare bell opto boards.