Skyworth LCD TV 37L28RM light is not on boot maintenance examples (with picture drawings) - appliance repair - Huaqiang electronic network
Today, I was working on repairing a Skyworth 37L28RM LCD TV that had a fault where it wouldn’t turn on. The green indicator light was on, but the entire unit was unresponsive. The standby button didn’t change its state, and the power board output voltages—5V, 12V, and 24V—were all normal, which indicated that the motherboard was receiving the correct power-on signal. However, there was no output for other key voltages such as 1.25V, 1.8V, and 3.3V, except for the 1.8V from the main chip.
The input voltage for these voltages was 5V, which is generated by U28 (a DC-DC converter). When I checked the output of this circuit, it was only around 1V, which was clearly abnormal. No visible issues were found during the initial inspection. To quickly determine the problem, I used an external 5V regulated power supply to test the circuit. After applying the 5V, the backlight turned on briefly, and the screen displayed for a few seconds, indicating that the rest of the motherboard was functioning properly.
This led me to conclude that the issue was in the 5V power supply circuit. I immediately focused on checking the U28 power circuit. Upon measuring, I found that the voltage at pin 1 of U28 was very low—only a few volts. This suggested a possible issue with the external resistor or capacitor controlling the output voltage. I suspected the capacitor C381 and tested it, finding that it was leaking.
After replacing C381, the 5V voltage returned to normal, and the TV started working correctly again. The repair was successful, and the unit was fully functional once more.
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