Bosch HBC86P753B/01 Combi Oven and Microwave, Stops after 3 Secs

[Thorpem]

Hi Folks,

I could really do with a bit of help in diagnosing a Bosch microwave issue

The model is: HBC86P753B/01 Combi Oven and Microwave. 

https://i.pinimg.com/originals/5d/7b/5d/5d7b5dd4a9d9cec46429852d96d23147.jpg

The problem only affects the microwave section:

The symptoms are as follows:

I power on and select microwave at any power level setting, adjust timer to 1 minute and press start, The light comes on fan runs for about 3 seconds and then display resets back to clock.

I am electronically qualified and aware of the high voltage risks, so dismantled to investigate yesterday. Magnetron shows no evidence of cracked magnets or distorted structure. Measures just under 1 ohm across heater with no leakage between either of the heater terminals and the case. If I run with the cover off, there are no sparks, unusual sounds or smells of burning.

The conventional oven responds correctly to door switch when opened.

This model uses an inverter PCB rather than the traditional capacitor and diode arrangement, so wondered if this module could be the cause.  As the part is quite expensive, I thought it would be sensible to seek advice first. Are there any other items to check, or has anyone experience of this module failing?

https://www.partmaster.co.uk/control-unit/product.pl?pid=1492093&query=HBC86P753B

Many Thanks

Regards

Mike

 

[AccApp]

Are you in the UK? We here in the US don't have anything like this in our market.

[Thorpem]

Yes UK, sorry I hadn't realised that this product was just UK market

Regards

Mike

[LearningTech]

 Iknow this is late, but....

we absolutly do Have things LIKE  this in our market.  ANY convection microwave for instance = heating element and magnetron in same box.   And many panisonic and bosch microwaves have  inverter tech. So.

i have seen that issue to be the inverter as well as the magnetron( yes even though testlike yours does it can still be bad) dont ask me why.

[Thorpem]

Hi, Thanks for trying to help me out.
I am very pleased to say that I eventually managed to resolve the problem and it is still working today.
I read in a UK forum that this model has a fuse to the inverter circuit which sits under the back cover.
The entry claimed that this slow blow fuse was prone to failure.
I sourced a replacement expecting it to blow again straight away and here we are several months later
with the unit still performing well.
(Cost of repair £1.25). Nice outcome.

[LearningTech]

Well glad it worked