Original post by: publius ,
I have two of these microwaves. They both had a failed relay on the control board. It is labeled Lamp Relay (RY1) on the schematic. It's inexpensive and available from electronics suppliers, such as Mouser or DigiKey. When it fails, the timer still works, but the light, fan and turntable will not work. The failure also disables the magnetron. Note that both of the relays on the control board switch the "neutral" side of the line, but that's no guarantee that they don't have 120V on them due to some other failure, since the neutral is floating. The magnetron is controlled by these relays, plus two of the three door switches. Never stick ANYTHING inside an open microwave cabinet without first grounding the terminals of the high voltage capacitor with a screwdriver blade. Short the terminal with the diode on it directly to the chassis ground. I then short both terminals together, just in case the transformer primary has an open circuit. You can test the filament in the magnetron and the windings of the transformer with an ohmmeter. You must disconnect the wires to do so.