Line-in on TV sets

[KARL]

TV sets usually have three "in" sockets for "video" and "audio-R" and "audio-L" (coloured yellow,red,white) which are linked/processed when you switch the TV to "AV". Why is it that a standard audio output from the headphone socket on, say, a personal stereo (cassette or CD) won't play through the speakers on the TV by connecting the cables to the line-in sockets and selecting AV mode - volume even on full ?

[landie]

Bear with me on this.

I have my TV set up as quadrophonic by connecting cables from our Hi-fi speakers to the external speaker connectors on the rear of the TV.

When I play the hi-fi I also get sound through the TV speakers.

[rojash]

You don't say exactly how you are connecting from the headphone socket to the audio in sockets, but in theory (if connected correctly ) it will work fine.

[KARL]

Using a purpose made cable, jack plug into the source, the red and white plugs into the TV (including the yellow creates blips on the screen) - the cable works (I have checked it separately) and so do the sockets on the TV. I agree with the sentiment regarding the theory, but it doesn't work all the same.

[KARL]

The answer has revealed itself: The audio sockets are disabled unless a true video signal is plugged into the video socket - there must be some sort of logic within the set's circuitry that prevents the audio being usable unless a signal (blank or picture, so long as it is a signal) is input. Whether this is unique to the set I am using I cannot say.