Konka LCD TV LC32F1000PD automatic shutdown maintenance example - appliance repair - Huaqiang Electronic Network

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After repairing a Konka 32-inch LCD TV, the cold boot image and sound were normal, but after a while, the TV would automatically shut down. The indicator light would not illuminate, and there was no picture or sound. After disassembling and checking, I found that the 12V output from the power board was stable when the TV stopped. This led me to suspect a fault on the motherboard. I tested the DC-DC chip N805 SY8123 on the motherboard, which converts 12V to 5V. I noticed that the 5V voltage was unstable, fluctuating occasionally up to around 7V, causing the TV to shut down. A fluctuating 5V is usually due to an issue with the feedback resistors—either the upper resistor has increased in value or the lower one has decreased. Visually inspecting the FB pin of the SY8123, I noticed that resistor R817, which is the upper sampling resistor (62K), had darkened in color, indicating potential damage. Using an air gun, I blew off the area and tested the resistance. It varied between 62K and 100K, confirming the problem. To fix this, I replaced R817 with a series combination of a 47K and 15K resistor, which provided a stable 62K value. After replacing it, the TV worked perfectly without any shutdown issues. The 5V output became stable, and the system ran smoothly. I've attached several images for reference: the TV model, the fluctuating 5V voltage, the physical layout and circuit diagram, the replacement process, and the final test results showing a stable 5V output and the TV working correctly.