The microwave oven, the main control circuit and the high voltage circuitry from the low voltage circuit of three parts, the computer. After the closed door, after door interlock switch S1, door monitoring switch S3, the magnetron thermostat S4, microwave power relays, transformer T1 primary, the secondary output of 35V, 2000V two AC voltage, 3.5V to MAG magnetron filament power supply, 2000V high voltage fuse after HVFUSE, the high voltage capacitor C, a diode D consisting of high pressure half-wave voltage doubler rectifier, generating a high voltage of about 4000V DC to the cathode of the magnetron MAG, MAG 800W microwave emission to heat transfer through the waveguide and transmitted to the furnace chamber, microwave food. According to the fault analysis of phenomena, low-voltage circuits and computer control circuit normally determine the fault lies in the high voltage circuit. Power, open the shell, insulated screwdriver with a strong short-circuited at both ends of the C discharge phenomenon, indicating that C is normal. Then detection T1, HVFUSE, D and MAG and other components found MAG filament circuit, resulting in emission of microwave magnetron can not cause the malfunction, replace MAG (Model 2M226), the power test machine, microwave normal troubleshooting.Lkxservice manual download site