zanussi 885x fault

The main oven turns itself off for no apparent reason. This started when the unit was two years old and, was eventually fixed under warranty – four visits and three months by ServiceForce. Two years on the exact same fault has manifested itself again.
The overheat thermoswitch has been replaced, no effect and, they think ??? – that maybe the control board is at fault, but not sure!!

Among the many parts that were changed two years ago was the main control board, this costs £120 + I am reluctant to throw good money after bad!

Is there any source of written material – circuit diagrams or testing procedure for these boards ?

Anyone have any ideas/suggestions 😥