I got for repair Panasonic TX-L42D25B. Symptoms: When TV is turned on, the green status LED flashes rapidly for a few seconds, then TV flashes the screen for a second and goes into standby. Red LED starts to blink 4 times in a row.
The service manual indicates that 4 flashes point to a SUB_F_12V failure. I checked 12V supply and found it to be steady at ~11,8V while the set tries to power on (green LED blinking), then it turns off as the TV goes into standby.
To try and isolate the problem to a single board, I started disconnecting cables to other parts of the TV one by one. Nothing changed by disconnecting T-CON board. When I disconnected the XW board the blink code changed to 7 or 10.
However, when I disconnected one of the LED backlight cables, the TV started up and worked perfectly fine. Except the screen was bright at the top and dimmer at the bottom.
So I disassembled the screen to check the backlight LEDs. I'm attaching pictures of what I had found. One LED was visibly damaged at one corner. However, a lot of other LEDs have some oxides or something "growing" from their legs in a fractal pattern, like branches of a tree. Even a lot of the LEDs at the top which are working seem to be growing these "branches".
I have never seen this before. Does anyone know why it is happening?
The service manual indicates that 4 flashes point to a SUB_F_12V failure. I checked 12V supply and found it to be steady at ~11,8V while the set tries to power on (green LED blinking), then it turns off as the TV goes into standby.
To try and isolate the problem to a single board, I started disconnecting cables to other parts of the TV one by one. Nothing changed by disconnecting T-CON board. When I disconnected the XW board the blink code changed to 7 or 10.
However, when I disconnected one of the LED backlight cables, the TV started up and worked perfectly fine. Except the screen was bright at the top and dimmer at the bottom.
So I disassembled the screen to check the backlight LEDs. I'm attaching pictures of what I had found. One LED was visibly damaged at one corner. However, a lot of other LEDs have some oxides or something "growing" from their legs in a fractal pattern, like branches of a tree. Even a lot of the LEDs at the top which are working seem to be growing these "branches".
I have never seen this before. Does anyone know why it is happening?
Attached Files
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