zannusi t/d keeps knocking off

hi
a customer rang re this machine she had a replacement motor fitted due to stopping after a few mins, it then apparently worked for a week or so
and began with same fault so she requested a new machine which she is waiting for, however she asked us to repair the old one as it was suggested that the pcb is the prob, its one of those jobs i am not too keen on getting involved with, has anyone had similar experience and any idea how much a control unit is likely to cost its a zdc 67550w p/no 91609616904