The microwave is making a loud humming noise when it is on and it isn't heating. It also has a burning smell. We had this microwave repaired replacing the magnetron and diode in Jan. 2006.

If your microwave is making an unusual or loud humming noise, you may have a problem with the magnetron. This component is part of the high voltage circuit and provides the microwaves that generate the heat. If the magnetron is defective, it may cause a loud humming or buzzing noise.
https://www.fix.com/repair/appliance/microwave/unusual-noise/

The loud noise and no heat means that the magnetron has failed. It the part that generates the microwaves that heat the food. When it fails it shorts out, causing the transformer to heat up. That is what was causing the burning smell. The cost of a replacement magnetron is around $130-150 range so it may not make sense to have it fixed.

Hi,
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Microwave Oven Basic Troubleshooting Tips

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Loud hum is usually due to faulty hv diod, resonance capacitor, or the magnatrone feed thru capacitor , chk it with a ohm meter , one by one n replace it .. zaheer Islamabad

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you have done well out of the oven . it sounds that certain components are well worn and probably no able to get parts best advice it time to buy a new one

the magnetron the unit has gone bad.sometimes there is burning smell as u mentioned.it is little expensive repair arond $ 150.00.find out the price of new unit plus iistallation/delivery chg and then make a decision.

humming sound is your magneto going out Dont have any idea of the cost for replacement however it may be cheaper to purchase another microwave than to repair this one. Good Luck

Dave

You either have a bad magnetron tube (5 or 10 year parts warranty item through GE Factory Service 1-800-432-2737 or www.geappliances.com) or a shorted high voltage rectifier. I think the light being out is a secondary problem.

Sounds like you just fried your magnetron. Normally when they go bad, they make a very loud noise like what you described. The smell concerns me because you may have ruined the waveguide as well. If the magnetron burns through the protective painted surface of the waveguide, the waveguide is ruined. In most microwave ovens this means replacing the entire unit because the waveguide is not replaceable. Putting a new magnetron in a damaged waveguide will result in the same arcing and eventual failure. In addition to the magnetron, the following components are part of the same high voltage network: HV Transformer HV Diode HV Capacitor Magnetron Thermal Cut-Out Any one of these components could have also been damaged. I DO NOT recommend taking any voltage measurements inside the HV network. Potentials of over 4000 volts can be reached and make it very dangerous for the do-it-yourselfer. Taking resistance readings with the unit unplugged is strongly encouraged. If you decide to pursue a repair, inspect the magnetron tip and inside of the waveguide first. If the magnetron is melted and/or there are burn marks inside the waveguide, a new microwave may be a in order. This actually may be a better option than an expensive repair. I hope you find this advice helpful.