After the power is turned on, the indicator light is off. Check that the 12V voltage output from the power supply board is only 4.6V. Disconnect the power supply board from the power supply board to the power supply cable of the main board. The 12V output voltage is still abnormal, so it is judged that the power supply board is defective. Detecting the load rectification output without short circuit condition, and then detecting the VCC power supply of UP101 (NCP1251) at 12-14V hopping, and the DP201 and UP101 of the cistern detection have not found any abnormality. When the voltage regulator circuit composed of UP808, NP203, and UP101 is mainly detected, it is suspected. The performance of the UP808 is not good. No obvious abnormalities were found after testing the resistance. The fault was eliminated after replacing the UP808.