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Konka 1486E TV, Picture OK, No audio from tuner, External AV audio OK

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.