Re: Duff microwave oven

The HV rectifier. It may just be the fuse though, 2A and under tend to self blow in time.

NT

A shorted HV rectifier or shorted HV capacitor would blow it.

Also, if the magnetron has somehow suffered a catastrophic internal failure, it might end up with the anode and cathode shorted, but that seems unlikely.

Well I am sure I can test a rectifier, but how to test the cap?

I am happy to throw a few quid into getting it working but I do not want to bugger around for days on end with the thing.

It's at my parents house and my Dad can get a couple of these ordered before I go back there

Where microwaves are concerned, replacing the fuse is the quick simple diagnostic job. It will probably be on the low voltage sde, not the HV.

Other options are replacing the transformer or the magnetron, if there is definately no heating effect.

ARW expressed precisely :

You cannot really test them properly, without the test voltage needed for the test - just put another fuse in.

It's a 5kV fuse!

Ouch - very unusual..

They usually only protect the input to the transformer, where the current is more sensible for fuse ratings.

Not for microwave ovens it seems:-)

I think the HV side is always protected, and it has to be very closely fused too because the transformer can't generate much extra in the way of a fault current.

Simple, short the dead fuse & plug in. Nuke HV fuses just protect against fire risk from prolonged overrunning of the transformer. Testing it for a minute won't get it anywhere near hot enough. And millions of nukes have no such fuse too. If its ok with no fuse, fit one and its done.

NT

Maybe these days - but not in our old clunker - circuit diagram:-

If that fuse had blown from fault current, i'd expect the glass to be blackened a little, also be able to see splatter from the wire opening under power.

I had the HV fuse blow on my nuker a few years ago, absolutely no signs of high current rupture, the wire was just floating disconnected from one end, fatigue from the vibrations of the magnetron and the fuse being unusually long for such a low current,

Well the replacement fuses arrived on Friday (I ordered two).

So today I went to my parents for Sunday dinner, tested the recitifer (it was OK) inserted the fuse and the microwave worked.

BTW Can anyone guess who made the front page of this weeks edition of the Sunday Express:-)? Clue - she was on the front page of last weeks edition.

Thanks for the input from everyone who replied. All sorted for £4 and we still have a spare fuse in case this one decides to just die.

Always test fuses before fitting :)