Here's a repost from the RCA DTA800 Digital to Analog TV Converter Box' thread:
Originally Posted by twey
Add a S-video connector (natually)
Add two ferrites as the EMI filter (or just bridge them) between two pairs of big pad just behind the connector.
Now, here is the key: Add one 10 Kohm as pull up straping resistor on R452. Locate at right of BCM3543.
I did this on a DTA809 (newer with passthrough). It looks like it have the same placement as DTA800. I ignored all the filter caps due to lack of test pattern to verify it.
I'm really glad I happened to run across this post. This is a great mod.
Yes, you can do this S-Video mod on a DTA-800B. I have two, and decided it would be worth trying on one of them.
It takes only 4 steps, and only one of the four (the last ) is very challenging.
1- Solder a wire between the empty position for L302 and L303 each (behind where the S-Video jack goes).
2- Mount an S-Video jack in the empty position on the board.
3- Drill out the case back for access to the plug (use the circle molded into the case as a guide).
4- Mount a 10k resistor in the empty position for R452.
As you can see (from the attached image), the resistor I used is much bigger than the ones that were intended to be used. But even then, it was very small. Unfortunately, it was still a little too small to fill the gap between the R437 dot (which is electrically common to one side of R452), and the other R452 dot, and too big to fit easily in the regular R452 position. I had to try three times to get the solder to 'mush out' to where it would contact both R452 dots. Working with components on this scale is not so easy, you'll need a lighted magnifier, and small soldering iron.
Use a pin to get contact on the pad surrounding the feed through hole for R452, and measure resistance from there to the common R437 dot to verify success.
I guess I could have used a regular 10k resistor, and run short tiny wires to the common R437 dot and the other R452 dot to connect it with. A dab of epoxy could secure the loose component and wires. Either way should work, pick your poison.
The the attached image shows a comparison between the S-Video and Composite outputs. It was obtained from an HD signal, photographed using simultaneous (side by side) displays of the two video outputs. The images consist of equal portions of what was about 25% of the 4:3 screen area.