How to repair a LG LED TV 55LE5400 mainboard in which the HDMI ports no longer work?

Hi Victoria. Try unplugging the television for 60 minutes then plug it back in. If the lines are gone? Try running a picture test. If this doesn’t work? Try resetting the tv to original settings or initial settings. If it asks for a password it will either be 0000 or 1234. This is if you can see the screen. I assume by your post that you have tried one different hdmi cable as well

Did you try repairing the PS with a repair kit first then replace both the boards after that?

The main power supply regulator section circuit fault. Either it will be a separate board, or the part of main board. Check and replace damaged component/s at its main power regulator [SMPS] section circuit. Contact any service technician. If you wish to get some details; check the site linked here. Pull up older posts.
http://electronicshelponline.blogspot.com/
It will be best to replace the power supply regulator board as card basis rather than making "Surgery" to it; which usually will make loss for both money and time. Even though you can make it right, it will cost around an amount equal to the cost of a new board; including the cost of (spare parts + service charge) More to say, most of the spare parts to it will be difficult to get from open electronic spare part market. This is true to most of the flat panel TV power supply boards; irrespective of its brand and screen size.

Sounds like 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 board is bad, replace the tv. funai tvs are junk

it is possible that either the lvds cables connecting the mainboard to the lcd panel are destroyed somehow or either the
Lcd panel itself has the problem could you provide some extra info a photo maybe so i can be more helpfull

it needs to be resoldered to the mainboard advanced help is needed

mainboard issue try updating first
if nothing happens try factory settings and after that replace mainboard or hd controller on you current mainboard

yes you have to replace the mainboard just buy the part yourself and install it there's not much to it buy the part @ www.shopjimmy.com

Could be numerous things such as faulty mainboard or powersuply board. If you have some electrical skills you can try diagnose the problem yourself and search youtube videos for more help and repair at home. But do it only at your own risk or hand it to profesional.

First of try different outlet.