The BenQ PB8235 projector does not appear to be energized, and the panel light does not illuminate. Open the inspection fuse is normal, measuring 370V output is only about 290, to determine that the PFC circuit is not working. Therefore, the power supply is mainly checked. The power supply of the PFC control board of the machine comes from the sub-power board. After detecting no voltage, the focus is placed on the sub-power board. The power board is composed of UC3843A driver K2101. After checking K2101 damage, the fault is still replaced after 7N80 replacement. Check IC6 pin has no output, 8 pin has 5V voltage, 1 pin only has 0.79V, normal value should be greater than 1V, lower than 1V IC The protection cuts off the output and begins to suspect that the IC is defective. There is still no output after replacement. Because there is no circuit diagram, the IC peripheral circuit is drawn by hand. After analysis, it is suspected that the optocoupler PC123 is damaged. After removing the inspection, it is found that the forward and reverse resistance between pins 3 and 4 is 1.7K, and the optocoupler is determined to be damaged. Since there is no PC123 at hand, the problem is eliminated after replacing with PC817. Ningbo Autrends International Trade Co.,Ltd. , https://www.supervapebar.com