Electronics > Projects, Designs, and Technical Stuff

Will a magnetron draw 480 Watts without radiating energy?

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AndersJ:
I have a LG microwave oven for repair.
It does not heat the material inside it.
But, it takes 480 W as if it is working.

Can the magnetron consume 480 W without radiating energy?
I.e. if current flows into the magnetron,
but it does not heat the material, does that mean it is broken?


TheMG:
A magnetron is a special type of vacuum tube and can suffer from the same failure modes as most vacuum tubes. It could be arcing internally, the vacuum seal could have failed letting some air into it, it can develop shorts to the filament, etc. All could cause the magnetron to draw lots of power without actually putting out much if any microwave energy. Additionally, if the magnets on the magnetron were damaged it could cause something like this as well as it wouldn't oscillate like it's supposed to.

Of course, first start by measuring for correct high voltage to the magnetron (~2000V typical, high voltage probe a must!!!). If this seems ok, then magnetron is faulty and will need to be replaced.

Also if it is a traditional transformer + voltage doubler capacitor setup (as opposed to modern high frequency inverter), check the cap.

wraper:
Pass through high voltage filter capacitor should be mentioned as well, it's an often cause of failure. It's a part of the magnetron but possible to replace.

Gyro:
Magnetrons can dissipate a lot of power internally when things go pear shaped. Here's an internal photo of a 900W Panasonic inverter one that I posted recently. It was still outputting some power, but it was dropping off very rapidly as it warmed up.



You can see that alternate Anode segments (the ones on the Antenna output ring) were in the process of melting down to cylindrical blobs. Not sure of the exact sequence, but the magnets had broken up, affecting the uniformity of the magnetic field, and the Aluminium cooling fins had become a loose fit on the outside of the Copper Anode body. There was a little dust, but ventilation was still pretty good. It was well over 10 years old though.

T3sl4co1l:
Also, is 480W inferred from an ammeter, or using a proper power meter?

Tim

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