Don't know, maybe this manual could help you. I had a similar problem.It started out of nowhere, with some sort of glitch... the picture would flicker and make a noise as that of interference... sometimes it would go back to normal, and some other times it just went black, but the sound was still there. I had to turn off the TV and back on to get the picture back. After having done some research on the net, I found that there was an easy way to check if the source of the problem was faulty inverters: I turned off the lights in the room and checked the screen with a flashlight at an angle... bam, the images were there, so I'm guessing there's a faulty inverter, or maybe both of them.
I have a LG LED Smart TV model # LA556205. After watching the TV for about 15 minutes the screen goes dark, the sound remains on. Turning off and back on, the screen goes back to normal for about 5 min, then goes dark again. I have taken the back cover off, but don't see any degradation on the capacitors and all the cables are tight on all connections. There wasn't any dust build up either.

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