LG 55ln5700 picture does not fill screen

Replace the jack wires going to the LED strips. Or look for the one bad jack wire going to the LED's and fix it. Use a volt meter on ohms to find the bad wire.

Why would you replace the power board for a burnt out backlight problem??

Sounds like the main board is going out. It tells everything when to do something and what to do. It even tells the power board to send power to the backlights.

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Logic card issue, get it repaired by a good technician. I too faced a similar situation

hi the led or leds has shorted in the panel, thanks

shaun

Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis. http://electronicshelponline.blogspot.com/ To some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement. To some models sets, the back-light inverter and SMPS section circuit will be integrated at its main board itself. If so; the main board should be replaced. To some models of sets, all these section circuit will be integrated at its main board. If this is the case, you have to replace the main board.

Testing TV Backlight LEDs - YouTube

? 4:44
https://www.youtube.com/watch?v=eEJoPCa7Kt0
Jan 24, 2015 - Uploaded by swappart.com
... explaining easy way to test individual LEDs on a strip from aTV backlight. ... Sharp LC-60LE820UN TV - LED Strip Testing - Long Version ...

IT02 - How to Test LED Backlight - YouTube

? 0:55
https://www.youtube.com/watch?v=YmSI2N6BGPA
May 20, 2011 - Uploaded by LCDPARTS
How to use IT02 to test Laptop screen LED backlight.

LST04-TV, How to test LED TV screen - YouTube

Not sure how you could have power coming out the cable in terminal, Ive repaired thousands of sets and have never seen that...how much voltage do you have there?

Back - light problem. Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
http://electronicshelponline.blogspot.com/
Some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement.

Fault to its main board. Short circuited component/s at it. Contact any service technician; or the authorized service center. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. http://electronicshelponline.blogspot.com/ . In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.