It's funny because I essentially took a crap shot from a page that described a Genesis 3 mod for either s-video, RGB, or both. I took a chance since it had the same CXA1645M as most Genesis 3 systems do. The page is here:
Link
Went to a Radio Shack and bought a .015 dia. silver-bearing solder, 22 gauge wire, a female s-video coupler, two 220uf capacitors, and some 68 and 10 ohm resistors (since I couldn't find 75 ohm resistors). Then went to a Wal-Mart and bought electrical tape, a cheap soldering iron, and a cheap hot glue gun.
Opened up the Genesis, took off the I/O shield, soldered the wires to the leads on the CXA1645M chip, soldered the resistors and capacitors as shown on the page, cut the s-video coupler in half, soldered the capacitors to the s-video coupler half, insulated the resistors and capacitors, cut a hole on the plastic shell, mounted the s-video, and grounded it to the I/O shield.
The hardest parts to the mod were soldering the wires onto the CXA1645M chip and mounting the s-video onto the case. The aid of a steady third hand was necessary to stem the risk of accidentally bridging a connection on the CXA1645M leads. The first modded system came out sloppy, but it worked. By the time my friend and I got to the third system, it looked as if the s-video port came out the factory like that.
Honestly, modding a Genesis 1 is much more work though the umass page details what to do pretty well. I bought a modified Genesis 1 system for about $5 only to find out that the mod was done sloppily. When I tried to fix it (again, using the umass page as a reference), I found that the modder had done some very stupid things during the modding process and that his needless and sloppy globs of solder were what were barely holding the job together. Unfortunately that Genesis had to be scrapped because it was unsalvageable.
Still, in the end, I got it working and I must say, the difference in picture quality is quite remarkable.
PS:
If you can, but a more fine conical tip. That combined with a third hand made modding it easy. Keep in mind, I did this with the help from a friend and a $5 soldering iron from Wal-Mart (found in the automotive electronics section oddly enough).