47" LG TV no sound no Picture model 47LN5700 took TV Apart Power board has no burn marks TV shows for a second LG when turned on then nothing Board # BD5PE628108011922(1.3) any help is appreciated

The led driver AND the T-con board are bad. If you could see a picture with the flashlight then the T-con board would be good. It is not. The led driver can be on the main board or the power supply board. You can get these parts from here: TV Parts Universal TV Stands DLP Chips ShopJimmy

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/ 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.

Main digital board fault. Check and replace it. If you wish to get more details visit the site linked here. http://electronicshelponline.blogspot.com/

Bad power supply board can burn out those led strips. Recommend replacing both board and strips at same time. Lg 47LN5700 UH TV Parts
You can order most of the parts here.

If you need further help, reach me via phone at https://www.6ya.com/expert/steven_a67ead41eb5fc62a

If you wish to get some details; check the site linked here. Pull up older posts.
http://electronicshelponline.blogspot.com/
http://electrotechnician.blogspot.com/

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://electro-medical.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.

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://electro-medical.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.

Check the following link and watch the video from the other link provided in that answer. It has a guide to isolate the failure to a particular board.
have LG 47in tv sound but no picture and can see an image Replaced the...

Check the power supply board first. All voltages have to be present and within 10% of the value printed on the board.

Seal deal w/ ours. I took it apart and the power supply board had the burn marks on it. Just ordered another power supply board (pn: 272217100571) for ~ $100. TV back panel comes off fairly easily to get at boards.