Why does the sound go off after some minutes of powering it?

@kelvinchinda there are a couple of things that can cause this. My first suspect is always the audio IC since those are not of great quality. Anyhow, you did not tell us what exact model your TV is. You've selected the LG Plasma TV 42PC7RV-TA as your device. For sound issues with that, you do want to go ahead and perform the troubleshooting according to the LG flowchart

It talks about no sound but it also applies to cases that lose the sound. Essentially it is the same check.

Now, if you get stuck on that, remove the back cover from your TV and take some really good pictures of your boards. That way we can look at those and verify (as well as mark) any issues we discover.

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