The PCB fuse rated at 10 amps blows. I've tried replacing the HV rectifier and the so called protection rectifiers across the HV capacitor.
There is no smell of burning or visible damage.
The magnetron, HV transformer and capacitor seem ok and the electronic control PCB seems to operate ok until the ac 10A fuse blows. The second fuse feeding LV to the PCB is OK and the microswitches on the door seem ok.
I've tested the transformer and its OK so I've still a problem with the oven and I'm £42 poorer - not very satisfied.