Microwave stopped heating. It whirrs and everything seems to work, but the food stays cold. Is this likely to be a faulty magnetron, which I assume would be pretty terminal for a 10 year old machine?
Are there any simple tests I can try before throwing it away?
It's built in, so quite expensive to replace. Maybe £200.
I had a couple trip out due to a faulty thermal cutout. A black cylinder about 10mm dia by the same in length, they have a collar to bolt them to some point on the steel casing and are n/c. They can be checked with an Ohmeter.
Pull the cables off the HV transformer and see if the control panel is energising the microwave unit.
Generally I believe that the usual failiure mode for the magnetron is a reduction in output over time. The only faults I have had in the HV section is the transformer going shorted turns, the smoke was a giveaway.
The circuitry is simple, but not really the best introduction to electronic servicing :-)
AB
First of all the magnetron and power supply are perhaps the most dangerous appliance of all to work on, with high voltages and high currents.
There are two types of power supply, inverter and transformer. The transformer type are remarkably simply with few components. More information is required.
As other posters have suggested there are thermal safety devices but there are also door switches and timers can also fail.
Not long ago I came across contacts on a timer that had overheated and because the plastic housing distorted the contacts would no long come together and supply power to the transformer.
I have also swapped magnetrons with success.
A lot of the time it's easily fixed. You need to narrow down the problem by giving us some info - that means you testing with it live, and did I menti on the power in it can kill a queue of technicians. Up for it?
NT
But remember there are some very high voltages. Many faults are the rectifier and voltage multiplier systems. Often a fuse blows if this part dies. I do not know if you will be able to get spares for a ten your old machine though. In my experience, unless they have been abused by running with no food in them Magnetrons outlast the devices they are in. Brian
No, I realised the danger, and I am afraid that, after a poke around to see if there were any obvious loose wires, I have binned it.
If you have a plug-in power meter, a simple and safe first step is to check the power consumption when the unit operates.
If it's just a few watts, enough for the turntable motor and light, then the magnatron is not working: possibly one of the fuses has blown.
Did you not check the HV fuse?
That wont always help.
Magnetron and HV rectifiers often fail short-circuit, so there will be an increase in consumption, but not by a great amount as the transformer operates close to saturation when working normally.
Many ovens these days have dispensed with the HV fuse.
Somehow I dont think you need a plug in power meter. What is it going to tell you?
A. The thing is consuming no power, seems fairly obvious already really.
Or B. The unit is consuming a kW of power with no obvious route of dissipation.
If the latter, the poor old GB has a major problem with his nervous system. Around 4A at 240V in something the size of a domestic microwave isn't going to sit there in a state of resonance methinks. Something will get hot and you wont need a power meter to detect it.
AB
Afraid not!
The HV fuse, if it has one, is one of several places the stored kilovolts s ometimes lurk.
NT
And easily enough to safely discharge.
ts sometimes lurk.
Of course. I would not recommend it to an OP that doesn't know what he's do ing though, that HV is transported to places in there that someone that doe sn't understand how they work would not realise. And it won't just give you an ouch.
NT
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