Some time ago mine (unbranded) stopped working too. I opened it and, to avoid the nasty radiation, I disconnected the cables that powered the transformer and magnetron. When I tested those cables for power (to see if they where delivering it when it was supposed to) it was intermittent, depending on the contacts position. Diagnostic: faulty contact leads. It could have been anywhere upstream the HV transformer and, therefore, fixable without messing the dangerous stuff (assuming you already have the proper respect for the 220V), but it was just a bad contact :) If nothing found there I would not have gone for the magnetron either... too risky.