The circuit diagram of microwave oven is shown in figure 1, which is mainly composed of low-voltage circuit, computer control circuit and high-voltage circuit. When the oven door is closed, it passes through the primary door interlock switch S 1, the door monitoring switch S3, the magnetron thermostat S4, the microwave fire relay and the transformer T 1, and the secondary outputs two groups of AC voltages of 3.5V and 2000V, with 3.5V supplying power to the magnetron MAG filament and 2000V passing through the high-voltage fuse tube H.V.FUSE, which consists of a high-voltage capacitor C and a high-voltage diode D.. The cathode of the magnetron MAG applies a DC high voltage of about 4000V, and the magnetron MAG emits 800W microwave, which is transmitted through the waveguide and emitted to the furnace cavity, and the food is heated by the microwave. According to the fault phenomenon analysis, the low-voltage circuit and computer control circuit are normal, and it is judged that the fault is in the high-voltage circuit. Cut off the power supply, disassemble the shell, and short both ends of C with an insulated screwdriver, indicating that C is normal. Then the T 1, H.V.FUSE, D, MAG and other components were tested, and it was found that the MAG filament was broken, which led to the failure of the magnetron to emit microwaves. After MAG (model 2M226) was replaced, it was turned on and debugged. The microwave oven was heated normally, and the trouble was eliminated. ?