Good morning: It seems that the television that says it carries the JYM-710 chassis, of which there is very little information, which also has several versions.
What may be happening, as I see it, is that I have dramas with the audio processor, I had failures related to this processor, which identify faults similar to yours with a fault locator, bone at the time of failure If the audio is sprayed to this IC with the cold gas or the fault locator, the volume will arise again if this IC is in poor condition.
What is the chassis it carries? Is he the one I mention? JYM-710? Of this I repeat there are several versions, I remember a fault similar to yours, with a chassis of these, the TV turned on perfect, with a perfect audio level, which was lost after a few minutes of being on the TV, after After struggling for a while, checking welds, Etc capacitors, all of them in the sound stage, I decided to spray fault locator to IC / IA01 (LV1116N)
In other words, the fault is a thermal fault, when this IC suddenly cooled down, the audio returned; Well there may be other causes, I think you can check the buttons, renew the memory; I do not know if it will be commercial this integrated where you live, here they were expensive.
I mean change the sound amplifier IC? Well one step is already done, now if it is within your reach cool the IC that I say, I do not know how much a fault locator will be today, I do not know what this gas will be called in other parts of the world, if it is expensive, well , it will be for other repairs where the fault can be interpreted as thermal.
Change the integrated LV 1116N that colleague neg2013 told me and I am walking 10 Thanks to all