Hello , my name is Jack Perhaps I can help you with this problem but first i would have a few questions;
Is this tv connected to a cable box/converter,satellite receiver,digital converter etc ?Do you have other equipment like a dvd,bluray,games etc. connected to this tv ?
If so , do you have the same problem on those ?
Digital converter from com cast. Yes we have DVD connected to the TV. Yes same problem on both.
And you said that you just turn the tv off and on again and the sound is working again ?
If so , after you did turn it off and on again does it work for a while or do you have to repeat this every few minutes or hours ?
O.k and one last question ;
Did this problem start all of sudden or just slowly got worse , like the sound would get low and you had to turn up the volume or would get distorted after the tv warms up etc. ?
would get distorted after the tv warms up.
O.k then I`m afraid that this is a fairly common problem with the audio circuit on your TV's main board part # 75015755 .
This board cost around $220 to buy and that is when you can find it !
While waiting for your reply I did take a look as to where it might be available and so far could not find a supplier.
Right now I can tell you that this problem is caused by the audio output chip on that board but it does not affect the audio outs at the back of the tv .
Which means that beside replacing the main board , you could use those terminals labeled as "fixed audio out" to have the sound through a sound system for example.
Otherwise I`m afraid that the only other solution would be to replace that main board.