I don't know much about this...other than whenever me and my bro use games machines/consoles of any kind, it has 3 different coloured leads. Red white and yellow, and one of them does the sound I think, and the other two picture. I can't remember which, but perhaps you should just make sure that one of them isn't faulty.
Sorry if I can't be much of a (or any) help
EvF
Sorry if I can't be much of a (or any) help
EvF