Skyworth LCD TV 37L16HC does not boot. The first thing to check is the secondary power supply, which shows a normal 5V. When pressing the standby button, the system transitions from a red standby light to a blue on state, with 24V, 12V, and PFC voltages all functioning properly. However, the backlight remains off. Pressing the standby button again fails to switch it back to standby.
The next step was to inspect the motherboard. A problem was found with U32 (4435M), which had been soldered and had four pins broken. This component is a FET, and the broken pins are the gate (G) terminals. After replacing the part with a spare, the issue remained unresolved. Testing showed that the 4435M FET operates as expected: when the G pin is at a high level, there's no output voltage; when low, it outputs 12V. The input voltage was normal, and forcing the 4th pin to ground resulted in a normal 12V output, indicating this part is functioning correctly.
Continuing the inspection, we checked the various voltage levels on the motherboard. It was discovered that the 1.8V supply was at 0V. This voltage is provided by U78 (AP1513), a DC-DC converter. Testing revealed that the input voltage to AP1513 was normal, but there was no output. A resistance check around the component didn’t show any obvious damage. After ordering a replacement chip online and installing it, the 1.8V output returned to normal, and the backlight turned on. The remote control function also worked properly, and the audio signal from the connected source was clear and normal.
After testing for several days, the TV operated without issues. The repair was successful, and the unit was fully functional once again.
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