You can try channel 4 with the CECB and your TV, but I'd be surprised if that worked.
Addressing the round RF cable to TV part of your test.
If your TV has a button for S-VHS, then it most likely has MTS stereo sound decoding as well. Part of that stereo over RF format is something called SAP for secondary audio programing. It will default to main channel english if no SAP is present. But it can cause you to loose sound if a piece of equipment sends what it thinks is a second audio stream. Poke around your sound menu for Mono/Stereo/SAP/Auto (Or similar). This is the ony thing I am aware of that would let you hear the audio momentarily, then cut out (Heard commercials, lost sound when show programming resumed).
On the White/Red/Yellow topic. What ken was indicating is that that button sounds like your TV also has a round 4-Pin S-Video jack for video as well as a Yellow RCA baseband video jack. The round S-Video jack uses the White and Red for audio for both the Yellow RCA and the S-Video, and would be why you can hear but not see from the Yellow wire. Look for a button that says A/V or L1, or similar. Another method of accessing the Yellow video jack is to type "00" on the remote. There is no channel zero, so sometimes manufactures use that to access line inputs.
Hope this helps.
But personally, if these steps fail too, I'd swap that box for a new one.
Another thing that would help us help you would be to tell us the make and model# the TV is so we can get a PDF manual online and be more specific about connections and buttons.
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