Microwave hums, doesn't heat.


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Old 09-03-09, 04:24 AM
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Question Microwave hums, doesn't heat.

My GE Spacemaker over-the-counter microwave (JVM132k 004) suddenly started making loud humming noise (on top of other "normal" sounds that one hears during operation) and no longer heats. Is this toasted? Anything I can do to troubleshoot?

The strange thing is that my TV also blew out last night. I had heated food at around 9:30. Watched TV until 10:30. Switched TV off. Turned it on again and could see highly distorted blue and white picture only. And the picture didn't change while changing channels. Then this morning, microwave doesn't work either. Coincidence?

If I had to buy a new microwave, what is a good brand to go for? This one lasted for 16 years - not bad for builder's grade stuff.

TIA!
 
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Old 09-03-09, 09:04 AM
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Did you have a thunderstorm overnight where a lightening strike might have damaged your TV and microwave? Are your other electronics and appliances working OK?

There isn't much to service in a modern microwave. They are pretty much built to be disposable. As far as a good brand, I have a hunch almost all of them are made in China by a handful of companies. Consumer's Reports' last rating of microwave oven reliability indicated that there wasn't generally much difference between brands. They showed Kitchen Aid as the most repair prone and Frigidaire as the least repair prone, but the spread was not huge. For some reason, they did not rate Sharp, which is surprising. For overall performance, they recommended Kenmore, GE, Panasonic, Samsung, LG, and Frigidaire over-the-range models. So it appears about any reputable brand would do the job for you, it just depends on how much you want to spend for the bells and whistles.
 
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Old 09-03-09, 03:33 PM
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No thunderstorm or lightening that I heard or saw.All other appliances, including my computer and printers that were on through the night, seem to be fine.

There are threads on Google that mention to check the rectifying diode and HV capacitor. Since I know how to work with electricity (in particular, capacitors), I opened up the microwave (took the control panel off) to see if I can troubleshoot. Yanked off the diode and tested it using the diode setting on digital multimeter. It seems to be open (multimeter reads no voltage in forward of reverse directions). Now the puzzling part is that I read somewhere the following:

Open diode = no humming noise + no heat
Shorted diode = humming noise + heat

So I am surprised that I am seeing open diode instead of a shorted one (since microwave humms). Or is that my digital vltmeter is unable to test the high voltage diode?

In any case, this is a generic diode (HVR 1X 3, 12 KV, 500mA). Appliance parts guys are asking $33-$50 for it. I think that is a rip off markup - this should be not more that $3-$10. Any ideas where I can get these cheap?
 

Last edited by xtvius; 09-03-09 at 05:35 PM.
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Old 09-03-09, 08:36 PM
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Well, it seems my digital multimeter cannot be used for checking the integrity of the diode in a microwave even when used in the diode mode. This because we are dealing with a HV diode, and multimeter just doesn't have enough voltage to do its job. So it is expected to show open even when forward biased. But at least we know it is not shorted (otherwise the reverse bias would not show open). And if I was to trust what I read (humming = shorted diode), I can surmise that my diode is probably fine.

So now I took off the capacitor. I measure resistance across the leads, it starts from zero and increases to about 10M ohms. It never shows infinity (or off scale). Is 10 M ohms reading sufficient proof of capacitor being shot? Where can I buy these cheap?
 
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Old 09-04-09, 04:32 AM
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Hmmm, I keep learning more... The capacitor has an internal bleed resistor. Is the 10 Mohm that I am seeing the resistance of that resistor?
 
 

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