LG 47LM4600 backlight off

[nixaee]

Hello,

I have a LG 47LM4600 that I'm trying to repair. When you turn it on the LG logo comes on then the back lights go off, and I can see the screen only with a flash light.

I tested the voltages from power board to main board and all were good except power on was not 24v it was 3.3v.

The voltages going to the back lights are 16v and 54v on vc1. I thought it was a bad power supply board but same issue after replacing.

Any help is greatly appreciated.

[CapLeaker]

Re: LG 47LM4600 backlight off

It sounds like you have a back light issue.

[tvtimmy]

Re: LG 47LM4600 backlight off

Burnt out leds.

[budm]

Re: LG 47LM4600 backlight off

You will get a lot more helps if you upload good clear pictures of the whole backside of the TV showing all the boards, also pictures of the whole power supply board that is clear enough to read the pin out of the connector that goes to the power supply board.

"I tested the voltages from power board to main board and all were good except power on was not 24v it was 3.3v."
Power on pin is the PS-ON is the control signal from the main board to turn on the rest of the power supplies. You also have other control signals as well for the backlights circuit.

[nixaee]

Re: LG 47LM4600 backlight off

You will get a lot more helps if you upload good clear pictures of the whole backside of the TV showing all the boards, also pictures of the whole power supply board that is clear enough to read the pin out of the connector that goes to the power supply board.

"I tested the voltages from power board to main board and all were good except power on was not 24v it was 3.3v."
Power on pin is the PS-ON is the control signal from the main board to turn on the rest of the power supplies. You also have other control signals as well for the backlights circuit.

Thanks, here is some pictures

https://photos.app.goo.gl/pMFDAeNK4pebDDmR7

[budm]

Re: LG 47LM4600 backlight off

Are you sure you count the connector pins correctly? It seems like you do not understand the pin assignment of the connector, there are 24 pins total.
The connector has two column, the exposed pins as you can see from the top side of the board are for the printed pin names left column, I can see why you think PWR-ON is supposed to be 24V, it is not how they are setup, you have 24V pin and PWR-ON pin. To test the right column pins you will need skinny probe on the wire entrance side of the connector.
You should use the attachment function to upload the pictures instead of using the link to the site where the pictures are.
You need to report all the pin's Voltage reading in this format:
When TV is plugged in but the power switch is not activated.
P_DIM1 = xxx V
12V = xxx V
12v = xxx V
3.5v = xxx V
3.5v = xxx V
24V = xxx V
PWR-ON = xxx V
ERROR = xxx V
P-DIM = xxx V
......
......

When TV power switch activated.
P_DIM1 = xxx V
12V = xxx V
12v = xxx V
3.5v = xxx V
3.5v = xxx V
24V = xxx V
PWR-ON = xxx V
ERROR = xxx V
P-DIM = xxx V
......
......