Siemens Washing Machine Repair Technology; Fully Automatic Drum Washing Machine, Not Heating
Fault Phenomenon: Power supply is normal, but when selecting the heating temperature, there is no heating.
Analysis and Inspection: The heating temperature of this machine is controlled by the CPU based on the temperature value of the thermostat THV. THV is a segmented resistor connected between C01 and B07 of the CPU. Due to the voltage division effect of the resistor, the integrated chip in the CPU uses the measured voltage value between C01 and B07 as the basis for controlling the heating temperature. If cold water wash is selected (such as Panasonic washing machine repair in Beijing), then THV is first set to zero position, its contact RF is disconnected, cutting off the circuit of the heater RR, and the washing machine performs a cold water wash. If hot water wash is selected, THV is set to the selected temperature position, RF is connected, forming a heating circuit: power phase line 66BRFRRTH90℃L2 (13-11) power neutral line. During the heating process, as the water temperature rises, the voltage value measured between C01 and B07 also changes. When the voltage value between C01 and B07 equals the corresponding voltage value stored within the chip, the CPU interrupts the power supply to B07, THV loses power, RF disconnects, cutting off the RR circuit, and stops heating. According to the analysis, first check that the heater RR is normal, and the contact RF of the thermostat is also normal. When powered on, rotate THV, and measure the voltage value at the C01 and B07 terminals of the CPU, which does not change (it should normally change). After power-off, measure the resistance value at the C01 and B07 terminals, and find that the thermostat THV is damaged.
Solution: Replace the thermostat.