Jul 6, 2020, 8:50 PM
Post #1 of 2
I got an old LG 47LD650 from a friend as it stopped turning on one day. The first thing I did was find a repair manual with the main board schematics, which I can try to upload if it helps.
LG 47LD650 Turns on in Sleep Mode, No Picture
When I press the power button the red LED in the lower corner of the TV goes from solid read to fad in/out. The power rails (20V, 12V, 3.4V) start supplying power to the main board. However the main board is not sending the signal to run the backlight.
I verified that the backlight and its power supply operate correctly by removing the INV_ON signal from the power harness and shorting it to 3.4V (also on the harness). This turns on the back light but the screen is black, as is expected as the TV doesn't send a signal.
The second way I verified that the power supply and backlight are operating correctly is the following. After replacing the pins that I used for testing the backlight I found the microcontroller on the main board that controls the power subsystem of the TV. Conveniently it has a reset button next to it, so I did the following.
- Power on the TV, which goes to sleep mode (I think), as the red power LED fades in/out. This also powers up most of the main board.
- Press the reset button by the microcontroller. This causes the backlight to flash for less than a second and the TV powers off.
- In the powered off state the red LED on the TV is on solid.
Anyways, as far as I can tell everything on the power supply board operates as it should but when I press the power button the the main board powers up and the red LED just fades in / out, no picture, nothing.
Any ideas as to what I could check next? I have standard electrical tools available to test, multi-meter, oscilloscope, etc.