Check whether the thermostat is bad, without loose connectors, etc., because of the possibility of failure of the control circuit itself is great. R × 1 block with a multimeter to check the thermostat wiring everything is normal. Analysis thermistor temperature sensor probe may damage will cause inaccurate temperature, causing the temperature control. Because of this thermistor resistance changes with temperature change (temperature rise, the resistance decreases and the temperature drops, the resistance increases), which is a thermistor having a negative temperature coefficient. Microwave fixed temperature control is based on the characteristics of the temperature sensor to the design. Check the thermistor is damaged, replace the same type of thermistor, microwave heat recovery.9u5service manual download site