I picked up a 5200 s-video mod board from ElectronicSentimentalities off eBay and installed it over the last couple weekends into my 4-port 5200. I first installed the power mod from console5.com since the video mod bypasses the RF module and that's where the power comes in on the 5200.
I decided to mount the video and audio ports on the little door covering the accessory edge connector. To make life easier (in the long run), I made the audio and video cables pluggable to the video mod board. The video cables running from the mod board to the A/V ports came out of an old custom mixer that was being thrown away at work. The cables are shielded and carry a red, black, and bare wire. I just used the red and black wires, so I used three of these shielded cables (composite, chroma, and luma). These cables were very stiff and difficult to shape/direct. If I were to do this again I'd use much more flexible cable.
I first tried using female machine pin headers to connect to the GTIA that way if the GTIA goes bad or I need to pull the mod board I don't have to break out a soldering iron. Unfortunately the connection, especially on pin 31 which is all by itself, was problematic. In the end I just soldered the wires to the GTIA pins. The cable from the GITA to the mod board is a little longer than it needed to be, but I wanted a little slack. The direction say you should keep the wires as short as possible to reduce the chance for interference with the signal. I'm not sure if the extra length hurts the signal at all, but it looks good to me.
I pulled the RF module, the PCB-mounted RCA jack, and a few other components in that area that are no longer necessary with the video mod in place. Early on I was thinking I might try mounting the mod board there and wanted to free up some space, but ultimately decided to mount it where everyone else who has done this mod mounted it. I may try mounting it there in the future, but I'll need to make a shielded cable to carry the video signals from the GTIA to the mod board. Perhaps something similar to what's there now, just wrapped in copper or aluminum foil tape.
Audio taps into resistor R50 and for ground I tap into a ground trace shared by R14, R12, and C18. I made a little plug for this cable as well. The mod kit comes with two RCA jacks even though the 5200 does not do stereo sound. I installed both RCA jacks, connected the audio wires to one RCA jack, then wired the second RCA jack to the first. The sound works great.
The mod board needs 5 volts so I found a filled via in the middle of the board that was on the 5v rail, sucked out the solder, and stuck a pin in there. I did the same for a ground point in the middle of the board.
I've mounted the board over the ANTIC and U1 and U4 chips. Since the ANTIC can get fairly hot, I put a couple small heat sinks on top and mounted the video mod board to the heat sinks using some double-sided tape. And since the board is between the ANTIC and U1/U4 chips, there's room for airflow underneath to (hopefully) not trap hot air and create problems.
With everything connected up I plugged it into my TV, fired it up, and amazingly it worked! The composite video signal is a hundred times better than the RF signal. Unfortunately I don't have s-video in on my TV, but I did have an S-Video USB stick and tried it out on my computer. The s-video signal is 100 times better than the composite signal. The image is crystal clear. Very cool!
Now for some pictures!
Here's an example of what it looked like before the mod. I used Popeye because that's the game that I've found creates the most noise/distortion.
And here's the composite signal on my TV after the mod:
Here's a view of the entire, modded PCB:
Here's the wired-up A/V harness:
And a close-up of the A/V jacks:
A close-up of where I tap into the audio on the PCB:
And a close-up of where I pulled 5 volts for the mod board. The ground pin is in the back.