First check the thermostat, and then check the latch microwave switches, such as normal, check the inside of the microwave oven microwave generator (magnetron) cooling fan. Inspection found that the fan blade does not turn, measure the resistance has to infinity (normal resistance typically 200Ω) with a multimeter, indicating that the motor coil has blown. The cooling fan is not running, leading to a microwave generator working overheating, resulting in 145 ℃ thermal switch action, so that intermittent microwave heating. After switching to the same type of fan motors, troubleshooting.TnNservice manual download site