Microwave oven fuse

Quite likely.

I am surprised the high voltage fuse didn't blow. That's what happened to mine - the magnetron had an anode cathode short and had to be replaced . That and a failure of the high voltage capacitor or the high voltage diode are really the most common problems, and are trivial to replace.

It is possible to remove the HT fuse mostly, and if the thing doesnt blow the mains after that, there are only 5 components on the HT side to check - the magnetron, the HT fuse itself, the diode the capacitor and the HT transformer. If THAT goes you are in trouble with likely magic smoke coming out.

You can check the magnetron off power by putting a resistance meter between cathode heater and ground. Should be open circuit. The capacitor you can use a resistance meter to see if the needle jumps and then goes back to open circuit.

The fuse is obvious to test but the diode is not - its stacked diodes in series and needs a few volts to turn on.

If the magnetro9n has gone its generally around 50% of the unit cost, or more, (somewhere in the £30-£150 range) and you should consider scrapping the unit.

Diodes fuses and capacitors are all sub £5.

Apart from that I found mine easy enough to fix, with the proviso you absolutely dont want to power it up with the covers off.

All in all its not worth the faff for a sub £100 unit, but mine was a £250 catering unit, and a £75 magnetron and a 90p fuse was in budget.

Very likely!

There some micro-switches on the door which are designed to make sure that the microwave cannot possibly operate with the door open. If the microswitches fail or are out of adjustment, the whole thing is designed to create a short which blows the fuse.

So you need to sort out the micro-switches before replacing the fuse.

Thanks for all that, interesting and informative. It did indeed blow the fuse again, with a an angry buzz, so I am just going to take it to a shop - if such a thing exists any more - and see if someone else can repair it.

Daniele

Economically?

Simply not worth it, Parts and labour likely to be more than its worth

There is a cost to /not/ getting it fixed . . . and indeed benefits to fixing it. Not always all about money . . .

Well there is a good You tube video about testing and fixing the high voltage side which is most likely what is gone.

The circuits are pretty much all the same - a high power high voltage transformer that drives the magnetron, with a winding for its heater, then a diode to rectify and voltage double the HT voltaqe and a fat capacitor to smooth it., and usually a fuse in it.

You test the capacitor for leakage with an ohm meter. You test the fuse for breakage with an ohm mketer. Unless you have 9V plus batteries in your meter you cant test the diode as its forward drop is about 7V (Its a stack of lower voltage diodes in series) but you can fake it with a 9V battery and a resistor and a current meter., You test the transformer for winding continuity and no shorts between windings or grounded wiring. If it is the transformer you are in for a hefty bill and trouble getting a spare.

Also be absolutely careful to see if the broken parts are in fact obtainable - a 15 year old machine is somewhat likely to not have a great range of spares.

And 'taking it to a man' is likely to incur a repair bill up towards £200 or a 'I cant fix that' response.

I forgot...

You test the magnetron for no short between the cathode/heater and ground, and for heater continuity. Magnetrons are also expensive

our local repair cafe sees quite a few faulty microwaves and fix over half.

Do they lose vacuum over time?

I dont think so. The article I read and my own magnetron failed with a soft short between anode and cathode. It also showed signs of rough treatment before I got it. I suspect metal was being deposited from the cathode onto whatever insulates it all inside, and eventually it arced over.

Don't forget there's usually a bleed resistor to discharge the capacitor. I've never heard of one going short-circuit, but you never know.

Not without first making sure it's fully discharged! If the bleed resistor has gone o/c and the capacitor's decent it could keep a charge for quite a time. At best you'd destroy the meter, at worst... :-(

When an old microwave oven went belly-up (magnetron died), I wondered if I could use the transformer. however, it seemed so firmly fixed in I gave up (perhaps a bit of self-preservation clicked in as well!).

Yep. When I tried to source a replacement magnetron I found I was looking at £50+.

If you get the model number of the *magnetron* rather than the microwave you may well find that a compatible magnetron is still available. When our

Tim

I started with that, and then the seller asked me what microwave it was for!

A lot of magnetromss sent back because they 'didn't fit' apparently

I found lower power ones as low as £35 and higher power ones in he £75-£110 area. I think mine was £85 from an Ebay seller. But it was a pukka branded Samsung unit.