Skyworth LCD TV model 37L16HC is experiencing boot issues. The first sign is that the indicator light is on but the TV won't start. The initial check shows that the secondary power supply's 5V output is normal. When pressing the standby button to turn it on, the 24V, 12V, and PFC voltages are all functioning properly, and the LED changes from red to blue when powered on, but the backlight remains off. Pressing the standby button again fails to return it to standby mode.
Next, the problem is suspected to be on the motherboard. Upon inspection, it was found that U32 (4435M) had a solder issue with four of its pins broken. This component is a FET transistor, and the four broken pins are the gate (G) terminals. A spare part was used to replace it, but the issue remained. The 4435M FET has the following pin configuration: the power supply input is at pin 123, the output is at 5678, and the control terminal (pin 4) is the gate. When the gate is at a high level, there’s no voltage output; when low, the 12V output is normal. After checking the input voltage and forcing pin 4 to ground, the 12V output was normal, indicating that this part is functioning correctly.
Continuing the inspection, various power supply voltages on the motherboard were measured. It was discovered that the 1.8V supply was at 0V. This voltage is provided by U78 (AP1513), a DC-DC converter. Testing showed that the input voltage to AP1513 was normal, but there was no output voltage. A resistance check around the component didn’t reveal any obvious damage. A replacement chip was ordered online, and after installation, the 1.8V output returned to normal, the backlight turned on, and the button controls functioned as expected. The sound from the connected signal was also normal. After testing for N days, the TV operated without issues.
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