Bosch CMA583MS0B/1 Microwave/Combi Oven Tripping & No M/Wave Heat

[jontymox]

Good afternoon all,

The above microwave does not heat, and is randomly tripping.

I carried out several tests at my customer’s prior to bringing the unit back to my workshop, as I was/am struggling to locate the cause/s of the above.

I’ve electrically and visually tested the transformer, and magnetron, along with the high voltage capacitor and diode.

The above all appear fine.

The power module appears to be suspect, as the voltage to the transformer is very low, but thought I’d ask on here if I should be testing anything else, before ordering a new board.

jonty

[electrofix]

ok first off its an isolation transformer and on side of secondary is to earth anyway so it has to be before transfomer

i would disconnect one of the wires to the transformer primary so you can play without the problems of high voltage

most likely causes of this is element and not microwave side

Dave

[jontymox]

Does anyone have a wiring diagram for the above that could be sent to me?

jonty

[electrofix]

only someone with Bosch tech access can get that. Dont know anyone on here with that

Dave

[jontymox]

I’ve done some further electrical tests, as advised by electrofix (Dave) and it does appear to be a board/relay fault.

Will provide customer quote, and update.

Regards,

jonty

[electrofix]

your tripping could be sparking relay contacts

solder in a new relay and take it from there

Dave

[SWERV]

Do you have access to the BSH order management system? they do have wiring diagrams and test procedures for each model now.

Merv

[jontymox]

Thanks Merv,

No access to the above BSH system.

In fact, I think I’m losing my marbles 😮

I decided to take another look at the fault/s and must confess that my test meter is faulty.

I thought some of the earlier readings were odd, (Ohms resistance fine) but very low voltage to and from the board to the transformer.

As Dave rightly stated, relays are either open or closed, leading me to recheck the above with an old analogue meter – which confirms 230 odd voltage to the transformer!

So, back to the drawing board when I have time tomorrow…

jonty

[electrofix]

ok that means you problems are on the high voltage side

fairly easy to diagnose that

but does not answer tripping problem as high voltage side cant cause that

Dave

[SWERV]

Might be worth checking for a leaky high voltage capacitor.
I can download the wiring diagram and send it to you if you send your email address.

[jontymox]

Finally found the fault… severely burned magnetron antenna, although Ohms resistance tested fine at customers’ and at my workshop!

I replaced the magnetron, and after a few seconds on a microwave setting serious arcing clear to see.

Looking more closely with the magnetron removed shows arcing has burned a small hole through the cabinet casing.

jonty

[electrofix]

jontymox wrote:Finally found the fault… severely burned magnetron antenna, although Ohms resistance tested fine at customers’ and at my workshop!

I replaced the magnetron, and after a few seconds on a microwave setting serious arcing clear to see.

Looking more closely with the magnetron removed shows arcing has burned a small hole through the cabinet casing.

jonty

you wont read any resistance reading as its just the antenna

with the hole in the casing it will probably be beyond repair

Dave

[jontymox]

Agreed,

Thanks to you, and Merv for your assistance.

jonty

[jontymox]

p.s I’m wondering what could cause such a drastic fault?

[electrofix]

can be various things including dirty waveguide cover or comtamination on the aerial

also customers dont seem to realise that its bad to turn microwaves on with nothing in it. those waves have to go somewhere so its more liklely to flash over

Dave

[Author]

Posts