LG microwave oven with poltergeist inside

That's some pretty thorough testing you've done so far, especially with testing the filament winding open and under load. It think it's safe to say the filament is good, and either the HV section has an issue or the magnetron is just bad.

Testing the HV part is a little trickier. Do you have a way to safely test the HV output from the doubler? If not, just skip this.

Next step would be swap parts, starting with the cheap ones. Swap the cap with a new or known good one, then try the diode. If that doesn't help, you probably have a bad magnetron, which may or may not be worth replacing.

This has some pointers, which you've probably seen already

It's a good doc for learning the concepts or experimenting at home, but sort of pointless for real repair work, where speed matters. For example, in a real shop, nobody takes the time to build a test jig for diodes. That would cost more than just replacing it, even if that's not the problem. Tapping into the filament with resistors seems weird too, since most places have a current meter, and if you're confirmed the HV section is good anyways, there's nothing left to replace but the magnetron, so proving that the filament resistance is 4% out of spec doesn't even accomplish anything anyways.

That is thorough testing.

One other thing to check is for cracked magnets on the magnetron. That can cause a no-heat symptom when everything lese tests good.

I've gotten original NOW/new magnetrons on eBay for under $20 so it's worth to simply replace. Then you'd have a spare if yours turned out to be good.

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** That sounds like pure bullshit and bravado to me.

Your first small mistake may well be the last time you breathe.

FYI:

Most microwave ovens are not worth repairing and certainly not worth risking anyone's life to repair.

I will never help anyone fool about with one of the horrible things and I think discussing such repair work should be banned on usenet.

.... Phil

Mine has needed two relacement magnetrons and four pairs of lamps in

32 years. It's a Sharp Carousel with stainless steel cavity and was worth repairing. Over 4 times the cost of a magnetron for a new one. (OK, new ones with painted steel cavities are only slightly dearer than the magnetron, but they rust to death in 3 years.) It really isn't beyond the wit of man to ensure the HV capacitor is discharged safely when replacing the magnetron or to screw in replacement lamps without bothering...

Hi,

Thank you for the inputs.

Answering your questions:

- no, I do not own any high voltage probe, so I will not test HV;

- I did not check for cracks in the magnetron so I will try this;

The oven is not the finest appliance on earth, but it does deserves a magnetron if that is the case. I just would like to be sure the magnetron is bad, because I am not willing to order a new magnetron just to find out the transformer is bad.

I do not own a repair shop, so it is kind of useless having expensive parts lying around as paperweights.

Had a little time to check the microwave oven again.

1) First, I checked if a short was developing in the magnetron between cath ode and anode (case) when the filament gets hot, but it doesn't. If you are wondering how I did it, I disconnected HV and connected a resistor from on e of the filament's terminal to case, and checked for voltage across the re sistor. Repeated this for the other filament's terminal;

2) Took the magnetron off. There were no cracks in the magnets (visible, at least) as Sam suggested;

3) Connected the filament (always HV disconnected) and powered the oven wit h lights off. The filaments clearly glows;

4) Checked HV transformer for signs of arcing or shorts, but none visible. Also, windings are not superimposed, they are placed side by side in the sa me leg, which somewhat reduces chances of arcing between windings;

5) Changed the HV diode for a new one (the cheapest part), but to no avail;

Now I'm stuck, and it seems my only option (unless you have a better idea) is to start replacing parts until the thing gets alive again. HV cap is sti ll inexpensive.

By your experience, which one fails the most: transformer or magnetron?

You don't have a HV probe to test for the - voltage at the diode? Jamie

Nope, I don't own an HV probe.

You really need to test the HV before proceeding to replace the magnetron. Do you have a tv repair place anywhere nearby? They would probably be willing to loan you a probe since they do not use them very often any more with solid state displays.

Geez, the magnetron is probably less than $20 on eBay.

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A yoke tester should have the proper ranges too- if it has the correct probe. None of the ones on ebay do.