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GE JKP90 Microwave burning odor - transformer primary?

microwave odor smell smoke transformer

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4 replies to this topic

#1 Protector01

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Posted 23 February 2014 - 10:56 AM

Greetings!

 

I'm working on fixing the microwave on my GE JKP90 microwave/oven combo.  It develops a strong odor of burning insulation within seconds of operating - yet it is working.

 

When I opened it up, I noticed that the black lead that connects to the primary winding of the transformer was brittle and crisped - it seems that this is the source of the odor.  That made me think that the transformer was drawing too much current to make the black primary lead burn up close to the transformer.  I assumed that the transformer itself was bad - there is what looks like a burned area on the secondary coil of the transformer, so I thought that the secondary of the transformer had shorted out.

 

The measured primary resistance is 0.6 ohms (test table says it should be between 0.2-0.4 ohms), the secondary is 113.5 ohms (measured to ground - test table says it should be between 60-90 ohms), and the filament resistance is 0.4 ohms (test table says it should be less than 1 ohm).  The primary and filament windings show infinite resistance to ground.

 

So, with the resistance measures for the primary and secondary being outside of the ranges listed by the test table, I ordered a replacement transformer.  After installing the new transformer, the symptoms are still the same...the microwave operates correctly, heats water as expected, but develops the burning odor within seconds of operating.

 

Has anyone seen something like this before?

 

Any ideas on how to proceed are most appreciated!

 

Thanks - Joe



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#2 Budget Appliance Repair

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Posted 24 February 2014 - 06:59 AM

I don't quite know how to describe it, but if it's kind of a sweet tangy burning smell, then it's the mag tube.

 

I don't work on microwaves much any more so I can't remember if the ones that had that smell still heated or not or just heated but not full power like they should.


William Burk (Willie)
Willie's Budget Appliance Repair
Eureka, CA 95501

#3 olyteddy

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Posted 24 February 2014 - 10:29 AM

For a GE the output test is 1 liter of water (they specify a GE plastic beaker, I doubt it matters) heated for 2:03 should rise at least 40 degrees F. 



#4 Protector01

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Posted 24 February 2014 - 10:49 PM

Sensei - Thanks for the comment!  I don't know if the magnetron is at fault - I don't detect a sweet tangy odor.  It's more the odor of burning insulation - and when I look at the components, the black lead that connects to the primary of the transformer is really overheating - just like if the primary coil was drawing too much current.  The weird part is that the microwave is operating - it is heating water.

 

Sohei - I didn't run the specific GE test.  for one thing, I don't want to run the microwave longer than a few seconds, as the burning odor starts up within a second or two when the microwave is operating.  While I only used about a cup of water in a plastic container for the test, it is noticeably hotter after just a few seconds of operation.  While it's not the official GE test, it does show that microwaves are being generated - perhaps too many of them!

 

Again - thank you both for your comments!

 

-Joe



#5 Budget Appliance Repair

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Posted 25 February 2014 - 08:33 AM

For a GE the output test is 1 liter of water (they specify a GE plastic beaker, I doubt it matters) heated for 2:03 should rise at least 40 degrees F. 

 

And just in-case anyone is wonder why the odd extra 3 seconds - that is the time it takes the mag tube to power/oscillate up to full power, (if you listen closely after pressing start on a microwave you can hear the mag tube power up with a light buzz noise).

 

-----------------------------------------

 

Protector01, if you're smelling that smell after only a second of running I can pretty much guarantee you it is the mag tube.  Unplug the two wires going to the mag tube and make sure the are well away from everything and then power up the microwave. 

 

With a high 99% probability, I don't think you will smell that smell anymore - of course it won't heat either.


William Burk (Willie)
Willie's Budget Appliance Repair
Eureka, CA 95501





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