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Do you get audio in TV mode if you tune around without regard for the picture signal?...if so sound and or picture alignment may have drifted away from each other which is fairly common on Dumonts and Dumont based crosleys and Stromberg Carlsons. If it's not the case and you can't get any audio in the FM band or TV band when in TV mode (Dumont sets will let you tune the entire TV and FM band in either TV or FM mode...the only difference between the modes should be whether the screen is lit and possibly gain level of the audio system) then you need to investigate the band switch particularly any sections that directly interact with audio or audio IF/detector stages before anything else.
If you have TV mode audio but it's fine tuning doesn't match the fine tuning of the video carrier there are 2 ways to deal with it: 1.) full alignment of the set which requires a 21MHz sweep marker generator, oscilloscope and skill, time and practice (it's often too involved to be worth while), or 2.) you can "walk" the sound IF alignment. If the set has good video response when fine tuning is set for best video then theoretically video alignment is fine as is. Walking the sound alignment basically goes as follows put up a test pattern that allows you to assess video bandwidth/fine tuning (multi burst or Philips PM5544 are especially good for this but anything can work) and an audio signal, tune for best picture then tune for best sound, then adjust tuning knob back towards best picture till you just barely have perceivable sound, adjust audio IF/detector alignment by ear for best sound at that tuning setting, then walk the tuning knob closer to best picture until you just barely have sound and repeat the sound IF alignment, eventually you will walk the tuning knob and sound alignment to a point where you have best picture and sound at the same point on the tuning dial.... I've done this on something like 4-6 different Dumont RA-103 sets and clones and it yields good results. You may go through 3-7 sound alignments in the walk before you're there depending on how far apart the 2 carriers are on the dial.
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