Well, I thought he just said they worked. Alright, let's try again: you plug in S-video from your computer and you get a decent picture, right? You plug in a composite source (VCR, say) and you get a decent picture, right? You plug in your coaxial cable and you get a decent picture, right?
If all of these are no, then go with what rich said. If one or more of these is no, but at least one of 'em works, it might be that some of them share something in how they're wired. (Like my technical know-how there?)
If you're getting some kind of effect with the component when you handle the cable, especially close to the port, I'd say it's a connection. Can't hurt to pull it open and look - no warranty on the thing. (Point of note: always check stuff out for what you're wanting, on location.)