Bosch HBC84E653B/04 – Microwave fails after 3 secs – replaced Mag, Inverter, fuses

[Nick_S]

Hi @electofix

I have just seen this same post thread from a few years ago

(https://www.ukwhitegoods.co.uk/forum…e-shutting-off)

I have a similar problem with the same model, an inbuilt Bosch HBC84E653B/04 combination microwave, grill and fan oven (about 12 years old)

All functions (both the grill and fan oven) work apart from the microwave

The symptom is when you hit the start button on the microwave, it starts to count down and then stops after 3 seconds with nothing heated up.

I have checked the door safety switches and they are all OK

I have replaced the Inverter and the Magnetron with working units

I have checked the circuit board and replaced both fuses and the then the bank of relays

But the problem persists

I even found another unit on eBay and did some checks on that (also blown fuses which I replaced) and then did some major component swapping

and the problem still persists

I cannot find any information on the Initiation checks but see that failing after 3 seconds seems to be a common fault

I am in a similar situation to Paul_A in that a replacement microwave costs about £700, and a combi would be more

However that is only 1/4 of the problem as my wife wanted 4 units when they were installed 12 years ago (2 ovens, 1 combi microwave and a steamer)

Now that the combi microwave does not work and the replacement units have a different appearance – so I would have to change all 4!!! at a stupid costs if they were to look the same and all work

Do you know what else is checked in the initialisation? heat sensors etc that could be causing the microwave to fail?

thanks Nick

[electrofix]

my next check on this one would be the 240v feed to the inverter

there is a small 2 pin plug on the inverter , a data cable and the leads to the mag

if you disconnect the 2 pin plug, this will disable all high voltage circuits but its always prudent to short mag to earth just in case

then you need to do a volt check on these leads while they are disconnected. you should get a 240v supply as soon as the microwave is energised

beware you are working on microwave circuitry. if the inverter is connected there are lethal voltages present

Dave

[Nick_S]

thanks Dave – very helpful and speedy – will check tomorrow

[SWERV]

One thing to check if you haven’t already done so is the fuse on the circuit board.
there should be two, you’ll probably find the 10amp fuse open circuit.

Merv

[kaibart]

On these older units I always change fuse inverter and magnetron at the same time if you haven’t this could be I’ve attached flow charts on where you should start

[kaibart]

And another 1

[kaibart]

And here is the other part

[Nick_S]

Hi Merv and Dave

Thanks for your replies

I have checked the fuses and replaced them where they were blown and also the capacitor that was bulging

BUT I don’t have any voltage on the inverter supply cables

Thanks for the logic flow charts – they should be very helpful

Any ideas how I put the machine into the debug mode?

Also is there a voltage trace diagram across the power board that I could use to determine what has stopped working ?

[SWERV]

When you say you replaced them with working units, were the parts new? and if so, were they the correct part numbers for your model?.

Merv

[Nick_S]

Hi Merv – I assume they are working units as they were new and they were the correct part numbers – the power board does not seem to be supplying 240V to the Inverter so I am not sure that the inverter or the magnetron are the issue as they are downstream of the lack of 240V

[electrofix]

double check fuses and also check all door switches

Dave

[Nick_S]

thanks Merv – fuses triple checked and both are OK

door switches checked and jumpered but will triple check these again (on my to-do list)

Keen to understand how to get the machine into Debug Mode – any ideas?

[electrofix]

could also be a dud power relay on the board

if you find the relay and solder 2 temp wires to the coil connections so you can look to see if its energised

Dave

[Nick_S]

I replaced all 4 relays in the bank with new ones on the power board
there is another one by itself – any idea which one it would be ?

[electrofix]

you would have to look whats controlled

Element
fan
lamp
turntable or wave stirrer
microwave inverter and mag
grill element
etc

not sure what yours has got as Bosch part site off at the mo

Dave

[Author]

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