A preliminary judgment fault in microwave circuits. Disconnect the high voltage transformer secondary circuit, hum decrease obviously, shows that high voltage transformer primary circuit works well, unplug the microwave power plug, high voltage capacitor, high-voltage diode is measured with a multimeter, protection diode and magnetron, found that magnetic field control filament and short circuit between tube and shell, caused by high voltage transformer working current is too large, so the "buzzing" sound. Replace the magnetron, troubleshooting.HiYservice manual download site