TCL LCD TV L32F2350 - No light issue, repair log and maintenance steps. The screen shows no backlight at all, but the red LED is on when powered on. Pressing the power button turns it off. When connecting a signal source, there's sound, but the screen appears dim. By adjusting the viewing angle, you can see a very dark image. From this, we can roughly assume that the switching power supply, main board, logic board, and LCD panel are all working normally. Since there's no backlight, the problem likely lies in the backlight strip or the LED constant current driver board.
After disassembling the unit, I tested the constant current board. The +24V power supply was normal. However, at the moment of power-on, the output voltage of the constant current board briefly reached +30V and then dropped quickly. This indicated an issue with the constant current circuit.
I adjusted the self-supplied constant current source to +60V and connected it to two LED strips. Both strips lit up properly, confirming that the fault was indeed in the constant current board. It also suggested that splitting the screen for testing could be unsafe if not done carefully.
A rough test on the constant current board showed some issues. Further inspection was needed, as shown in the following image:
After checking Q601, I found it had a soft breakdown. I removed it for further testing. Replacing it with a similar MOSFET resolved the issue. Here’s the replacement process:
After replacing Q601, the LED strip on the test unit lit up normally. I measured the main voltage for reference to ensure everything was stable.
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