SS40G/FS40 TV-Out not recognizing?

Trying to get TV-Out functionality on my SS40G shuttle. I got it secondhand
so I don't have the original TV-Out cable, but I'm using one that came with
a radeon card and it seems to have most of the pins (some of the middle
ones are missing, though I've read elsewhere that they may be audio pins?).

Anyway, I plug in my S-Video>RCA adapter, which is hooked up to a TV, and
it doesn't seem to recognize the TV. using some reference SiS 740 drivers,
I tell it to force TV display, but no dice.

Adapter/cable/tv are verified working with tv-out on my other pc.

Is there a special cable I need? What exactly is going on here?

Thanks,
John