I have a 7-pin and a 4-pin s-video cable. The 4-pin works, the 7-pin does not. Try a 4-pin cable, it might do the trick.
I'm like you, I just want to use S-Video output, but not why it does not recognize the screen almost never, sometimes, if I display an image, sometimes not. I would at least be able to use video is out but I had nothing connected. Let's see if we can help.
PD: Forgive my English but I use translator