Antonio F Miami , FL June 08, 2018 Appliance: Model KEMC378KSSO Humming sound and burnt smell I measured the resistance between the two connectors on the magnetron: should be close to zero ohms and it was. I measured between the same connectors and the metal case: should be mega ohms, it was 15k ohms. That is a bad, partly shorted unit. I also checked the resistance of the thermal cut off, which should be zero but was 10 ohms so I replaced. The HV diode is checked with a 9 V battery (YouTube checking microwave HV diode) and it too was bad. Make sure to take pictures as you disassemble the unit as I had a few leftover screws. Unit is working great now. Read More... 2 People found this story helpful Do-It-Yourself Rating: Repair Time Estimate: 30-60 minutes Tools: Screwdrivers