Two pieces of information are needed. At least one would help, but
both would be better.

Is the sound low when you use the AV jacks ?

Does the TV have an indication when it is recieving a stereo
broadcast ? Is it indicating a stereo signal ? On a Panasonic it might
not, but if you have a channel you know has SAP, you can try to switch
to that.

If it reads the SAP the level coming out of the IF strip is
sufficient, and if that is the case I'd say you have an 80% chance
that the AV jacks will have low sound as well.

In that case, if you lack a print, download the datasheet for the
audio output IC. Find out just where volume control is achieved.

This is all assuming this TV is stereo, if it is not, say so because
then there is an entire different direction to take.

JURB