A Skyworth LCD TV model 46E60HR belongs to the 8R80 series. The backlight turns on, but there is no sound and a gray screen appears during boot-up. There are no characters or logo displayed. Initially, it was suspected to be an issue with the screen or logic board. After opening the cover and measuring, it was found that there was no 12V voltage on the logic board. The resistance between 12V and ground was normal, and the fuse resistor wasn't blown. Following the LVDS cable, the power supply chip U2 for the 5800-H8K800-0000 screen was located on the motherboard. The input voltage was 12V, but the output was 0V. The problem seemed clear, but after checking the short circuit on both input and output of U2, the screen remained dark. This was confusing—was it really just the screen power supply?
After thinking carefully, the power supply for the LVDS large chip was measured, and there was no voltage. Then, the LDO-U6 chip was checked, and it had no input or output voltage. Without a circuit diagram, the circuit was traced back to the DC-DC switching power supply chip U1. The model was P3482. Checking the data sheet, it's an 8-pin DC switching power supply chip. Pin 2 receives 12V, while other pins are inactive. Pin 3 provides 3.3V/3A for the LDO and chip power. Pin 7 is the EN pin connected directly to 12V high level. It was clear that U1 was definitely damaged.
Since there was no P3482 chip available, a similar one, FR9888, was used as a replacement. After booting, U1 output 3.3V, and the screen power supply chip U2 output 11.88V to the logic board. Finally, the long-awaited Skyworth logo appeared on the screen!
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