Answer Roy, with the microwave unplugged and set for 10 minutes, the transformer WB27X10868, magnetron WB27X10735, and diode WB27X1160 will need to be tested. The transformer primary windings should measure .3O resistance, the secondary winding should measure 50-70O resistance. The diode would be tested for continuity in both directions, one way having continuity while the other way not. The magnetron would need to be inspected at the antenna tube to ensure that it is not burned out and tested for continuity from the filament if the tube to the magnetron housing. If these all test good, the failure would either be in the main control WB27X10871 or the capacitor WB27X10240. The capacitor can be tested for resistance and it should scale up towards infinite after starting with a low resistance, but this is not a guaranteed way to test the capacitor. Read More... Answered by AppliancePartsPros.com | Tuesday, April 28, 2020