Probably not worth fixing (kerb shopping) but if anyone has any ideas or has encountered a similar problem in the past then I hope you might help. Stop reading now if you think I might be wasting your time.
As stated in the subject line the TV is able to tune channels and display a correct picture. The problem is that there is no sound with that picture. To be correct there is sound but it is just static / white noise coming out the speaker. I've tried turning up the volume to try and hear any program material hidden below the noise but I think it is all hiss, and it doesn't change when changing channels either. The audio from the external AV input works fine so I think the audio amplifier stage is OK.
I don't have a schematic but I traced the audio RCA socket input and amplifier output lines to a big 56 pin DIP labelled TB1238AN. A look at the datasheet's block diagram has confirmed the pins for audio input and output. Pin 53 labelled "Limiter IN / H Correction" seems to be the next stop to check but somewhat poetically this is about the limit of my investigative skills. I'm not sure what type of signal I should be getting on the CRO at pin 53 nor do I know what kind of signal I should inject into this point to test the IC. From the datasheet it seems to me to be a dual purpose pin?
Perhaps this is enough information to confirm the chip is a dud, or maybe something is broken further upstream. Anyway, suggestions on where to go will be appreciated.