After repairing a 32-inch Konka LCD TV, the cold boot image and sound were normal, but after a while, the TV would automatically shut down. The indicator light didn’t illuminate, and there was no picture or sound afterward. Upon disassembling and inspecting, I found that the power board was outputting a stable 12V when the TV was off, so I focused on the motherboard for the fault.
Testing the DC-DC chip N805 (SY8123) on the motherboard, which converts 12V to 5V, I noticed that the 5V voltage was unstable, fluctuating and occasionally rising to around 7V. This instability caused the TV to shut down automatically. A common cause of such voltage fluctuations is a faulty feedback resistor in the voltage divider circuit.
Visually inspecting the FB pin resistor R817 (62KΩ) connected to the SY8123 chip, I noticed that the resistor had darkened in color, suggesting possible damage. Using an air gun to clean it, I tested the resistance and found it varied between 62KΩ and 100KΩ. This inconsistency confirmed the issue.
To resolve the problem, I replaced R817 with a series combination of a 47KΩ and a 15KΩ resistor, totaling 62KΩ. After reassembly, the TV functioned normally without any shutdown issues.
Here are some images from the repair process:
- TV model
- 5V voltage fluctuation
- Physical layout and circuit diagram
- Replacement of R817
- Post-repair 5V output test
- Final working condition of the TV
This repair shows how a small component like a resistor can significantly affect the stability of a device. It also highlights the importance of careful visual inspection and testing when troubleshooting electronic circuits.
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