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Bryan, Home Appliance Technician
Category: UK Appliance
Satisfied Customers: 12156
Experience:  EPA Certified HVAC
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bosch microwave HME5680 main fuse blows shortly after microwave

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bosch microwave HME5680 main fuse blows shortly after microwave is started
Did you say you replaced the HV transformer ? or just the diode ? is it the house fuse blowing or the internal fuse ?
Customer: replied 4 years ago.

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.

it wouldnt be a switch. the high voltage transformer is drawing above 10 amps, this is the issue. and the magnetron wouldnt blow the fuse. the transformer itself needs to be replaced, this is not uncommon on these. you have to replace it. wish I had better news, these can be expensive. sorry. thanks , Bryan
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Customer: replied 4 years ago.

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.

how did you test the transfromer ?
Customer: replied 4 years ago.
Transformer removed from case and primary supplied with a variac and clip on ammeter. Magnetising current measured at intervals to 240v when some saturation was commencing and the current was just under 2 amps. At full voltage, the filament voltage was about 3v and I did not measure the HV but there was no discharge or change for about 10 minutes. I intend to repeat procedure with transformer supplying the HV load I.e. magnetron and capacitor in situ gradually raising the primary voltage and monitoring the primary current until full voltage is reached. I will power the oven normally as well to cool the magnetron and include a water load in the oven. If the PCB 10A fuse blows when I initiate the cooking cycle in this mode of operation I wll assume a fault in the door switches etc. If the transformer hums excessively as I raise the volts I will stop the test and investigate the condition of the capacitor, magnetron filament etc.
try reinstalling the transformer but leave the magnetron unplugged so your just powering up the transformer and not the magnetron. see if the fuse blows. if not try it again with the magnetron connected and see if it blows, if it does you may have a bad magnetron.