The microwave appears to be working normaly, but it is not heating. I have ohmed out the magnatron and it checks out fine as per the tech sheet. I am getting power 120vac to the primary side of the HV transformer, so I think it is bad.
Answer Hello Bryan,
Before beginning, unplug the unit and short both sides of the high voltage capacitor to ground to discharge any stored charge that could get you. Also, to avoid a false reading, anytime testing for resistance, at least one connector should be disconnected to neighboring circuits from fouling the reading. (Measure at room temp., or 70° F). Testing the secondary side of the high voltage transformer, you should read on the RX1 scale of your resistance meter, from 88O to 92O. From either terminal to ground should read infinity, (no contact). The same should apply to the other leads when testing to ground. The primary side of the transformer, where you read 120Vac, should read less than 1O. As per the manufacturer, the filament terminals, (the ones that connect to the magnetron), should read continuity. It doesn't state an exact reading so as long as it isn't open, it should be good.
Most of the time, when the high voltage transformer is shorted, you will hear a low frequency growl. This holds true for the diode causing the issue also. To test the magnetron, unplug the unit and discharge the capacitor. Between Terminals: Less than 1 O. Each Terminal to Ground: Infinite O. NOTE: This test is not conclusive. If microwave oven does not heat and all other components test good, replace the magnetron and retest. To test the high voltage capacitor, between Terminals: Meter should momentarily indicate continuity, then 9 MO (deflection). A steady 9 MO indicates an open capacitor. Steady continuity indicates a shorted capacitor. In either case, replace capacitor. Testing from either terminal to the case should read infinite resistance, (No continuity). To test the high voltage diode, the test meter cannot tell if voltage is being passed through the diode without voltage being applied. For this reason, a nine volt battery is normally used to test the high voltage diode. The test meter should read the nine volts in one direction and, by reversing the diodes’ polarity in the test circuit, it should not let any voltage pass.