The one datasheet I have is japanese the other is english. The way that encoder works is a bit like the old sony cxa1145. The cxa1145 outputs s-video and then inputs that s-video into other pins to generate composite video. It seems these old rohm encoders output yuv then input that yuv into other pins after passing the signals through a small circuit to generate composite video.
Thanks for the upload!
Yes, after looking at the datasheet for the 6591, it looks like the RGB comes in and gets converted to component (or Y, BY, RY as the datasheet calls it, assuming it's the same thing as yPbPr). The component outputs go through a small circuit, input back into the encoder, then converted to S-Video and composite. It looks like the 6592 does the same thing, though the external circuits might be slightly tweaked.
The real question is... does the 6594 do the same thing? As I've said, I have two SNESes with the 6594. One has it located where you'd normally find the S-RGB encoder, the other has it in front of the cart slot where the 6592 is located. Finding a datasheet for the 6594 has been impossible! Apparently you can pull the component output right off the encoder, so I guess I'll give that a try first to see if the 6594 actually outputs component like the 91 and 92 do.
After that, I doubt the component out is TV-ready straight from the encoder. Looking in the datasheet for the 6591, it looks like they give a schematic to output to a TV, but I can't make it out entirely. Doesn't matter though, things might have changed between the 92 and 94 versions anyway. I was talking to Jam about this and from what he understands the signal outputs should have an impedance of 75ohms. So I think what we'll have to do is measure the impedance of the component output then try our best to get it to 75ohms. I really don't have great knowledge of this kinda stuff by the way. Anyway, the schem from the 6591 datasheet might be a good place to start, but it's a little confusing.
The first thing I gotta do is find out if the 6594 actually outputs component. I think I'll give that a shot today. If it actually does, then we can go from there.