Hi everybody, happy new year! I'm back with a whole new stack of crusty old games to review, but first, I'd kick off 2013 with another howto. There are already a number of excellent step-by-step guides on how to mod the Genesis floating around the Internet, including the the one I followed, so mine will contain primarily general information and random musing about my own experience.
Use the info in this guide at your own risk. Like the NES, there are no dangerous voltages inside the Genesis, but it's vulnerable to static electricity once opened. You will be soldering wires directly to components inside the Genesis too, so take care not to cause a short circuit by bridging connections. Also, you need to know how to solder stuff. Probably should have mentioned that right away.
So what's so great about s-video?
dot crawl, color bleeding, and so on. In short, composite video kinda sucks.
S-video is an attempt to deal with this suckage by keeping luminance and chominance electrically separate. S-video passes Y & C from the source device to the TV set on their own wires, avoiding most of the image problems inherent to composite video. Of course, to take advantage of this, you need a TV with an s-video input. They're pretty distinctive, usually consisting of a round plug with four pins; one for Y, one for C and two grounds. They're commonly found in higher-end TVs made in the last couple of decades, though they're becoming increasingly rare as all-digital connections, like HDMI, have come to dominate.
S-video has been supported by video game consoles and old computers since the Commodore 64. The video encoder chip in the Sega Genesis supports it too, though Sega saw fit not to properly wire it up. No matter, we can lift the signals directly from the chip.
What do we need?
|Model 1 Genesis|
In addition to a model 1 Genesis, you will need most of these components to build the Y & C amplifiers. You don't need the LED, phono plugs or oscillator unless you would like to follow the author's complete instructions to overclock the Genesis' CPU and add A/V jacks to it. The project wires, transistors, capacitors, and project boards were readily available at my local Radio Shack, but I couldn't find 110k ohm resistors in stock, so I had to make due with 100k ohm pieces. A female s-video jack was the hardest part to locate, as Radio Shack no longer stocks them. Mine came from a breakout cable used to connect a PC video card to a television, but you can pick one up here for just a couple of bucks.
Dismantling the Genesis
Building the amps
The video encoder chip inside the Genesis, a Sony CXA1145, does indeed generate s-video signals, but not at a power level sufficient to directly drive a television set. We need to build a couple of simple one-transistor amplifier circuits to boost the 1145's s-video signals to a level high enough to drive the TV. David Howland's website provides excellent step-by-step instructions on how to turn a pile of parts into two functional amps, and I can't add much more. If you're having trouble following the circuit diagram, just do what I did: make your circuit board look as close as possible to the one in the image. The amp input lines shown on the circuit diagram aren't actually pictured and can be challenging to locate, so I've highlighted them in the following photos.
Connecting the whole mess up
|Up in this photo is toward the rear of the Genesis|
Next, you need to connect +5v power to the amps. You can lift that from pin 2 of one of the two voltage regulators. Pin 2 is closest to the front of the Genesis, though Sega has conveniently labeled all three pins on both regulators. You can connect the ground wire just about anywhere, like the RF shielding, but pin 3 on the voltage regulator is a good spot. I've found it's best to solder all connections, including ground, to guarantee a solid, noise-free signal. This would also be a good time, while the voltage regulators are exposed, to replace the blue thermal grease that couples them to the heat sink. After 20+ years, the grease tends to harden & lose its ability to conduct heat.
Now that the amps are wired, it's time to bench-test them. I used a USB TV tuner attached to a laptop as a test bed for convenience sake, but any TV or capture device with s-video inputs should work. If you get no picture at all, recheck pretty much everything. If you get a black & white picture, then luminance is working but chrominance isn't. If you get a picture with lots of vertical & horizontal hold problems, try reversing your Y & C signals. If the picture is visible but noisy or jittery, recheck the solder joints between the Genesis & the amp board you built, particularly power & ground. Once you've verified everything is working and you're ready to mount your amp board, be sure to insulate the bottom with electrical tape to avoid shorting it against any of the Genesis' components. The amp board can be taped or hot-glued to the mainboard in front of the cartridge slot.
So how's it look?
|The finished product|
Lightening Force. The red box around "Daser" shows significant dot crawl in composite video, but not in s-video. Composite video's "softer" look makes the planet in the background appear less jagged, but a lot of detail in its clouds and land masses is lost. Ironically, the Daser level in LF includes a sandstorm which partially obscures the player's view of the action. It looks much better in composite video than s-video because the checkerboard grid of pixels representing the sandstorm blur together, creating a translucent effect. This may well be an example of the developers using composite video's inherent limitations to their advantage.
So there you have it. With a little know-how and a raid on Radio Shack's parts bin, you too can enjoy the mighty Sega Genesis in vivid detail.
Thanks for reading my guide. Stay tuned for more classic game reviews!