Responding to a 46-inch Samsung LCD TV with a black screen failure. After disassembling, the PFC voltage on the IP board BN44-00341A is 389V, and the IP board outputs 12V to the main board, and 5V is normal. The main board outputs to the IP board's lighting control INVERTERON/OFF and PWM are high. Explain the fault in the backlight circuit and its load. Test the backlight ICLX6503AID 1 pin 12V normal, 16 pin VREF no voltage, and then test 7 pin EN enable is actually 0V! After the power is turned off, the test 7 feet are not short-circuited to the ground. Followed by the 7-foot print trace cleaning, found that 7 feet through the RI814 silk screen 01D resistors connected to the optic coupler PC803S 3 feet, and the motherboard issued the lighting control INVERTER connected to the PC803S 4 feet, obviously the fault should be the optocoupler PC803S 4 feet and 3 The foot is not connected.
The 1.2-pin of the optocoupler PC803S is printed and cleaned. It is found that the 2-pin of the optocoupler PC803S is connected to the K-pole of the UB801 patch 431, and the R-pole of the UB801 is detected whether the PFC voltage reaches 380V, and the PC803S has 1 pin. Through two resistors RI875 silk screen 30B.RI873 silk screen 30B connected to PFC drive power +14V. It was found that RI87530B=2K became more than 200K. After the replacement of the RI875, the test machine was successfully repaired. Thanks for watching!
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