I have a Maytag over-the-range microwave (model MMV4205AA) that suddenly malfunctioned while cooking. The humming noise normally present while cooking got at least twice as loud and sounded more like a pronounced vibration. Also, after about 20 seconds of loud humming, the microwave had a strong ozone/hot smell so I stopped it. The auxillary functions like exhaust fan, light, timer, turntable, etc all function normally. The cook function produces the loud humming and smell. The microwave is approximately 18 months old, and has a grounded 20A dedicated circuit feeding it. Any ideas how to proceed? Where do I start troubleshooting? Thanks.
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.
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