Sega Genesis RGB Bypass
PLEASE READ: The Genesis does not require a modification for RGB-output, simply a cable. This page is an “experts-only” page that shows how to bypass the Genesis’ internal RGB amp with a different one. All details are below, but this mod requires you to make irreversible modifications to your Genesis system. Beginner and intermediate modders should not try this mod!
This page showcases ArcadeTV’s Genesis RGB Bypass board, that can be installed into any Genesis console, as well as a Sega Master System (although a slightly different board is required for the SMS).
Why perform an RGB-bypass?
There are three reasons someone might want to perform this modification:
Jailbar fix: As shown in the picture above, performing this bypass removes all jailbars from the Genesis’ output image. Please note that there are many different, easier ways to remove jailbars, however doing an RGB bypass is the only way that works consistently across all models.
New RGB Amp: All Genesis and SMS systems use a Sony CXA1145 chip to amplify the RGB signal. The CXA1145 is an excellent chip, however this bypass uses the newer Texas Instruments THS7314, which has a high-quality low-pass filter that removes unwanted noise. Using the THS7314 isn’t a clear “better or worse” choice, it’s mainly a preference. Some might argue that the “ringing” the CXA1145 produces creates the specific look of the Genesis that we’re all used to and shouldn’t be changed. I’ll leave that up to you.
SMS RGB issues: I’ve had many people email me claiming their SMS won’t output RGB through the multi-out. I’ve also experienced this myself with my Japanese MK-2000 SMS. I found a few workarounds for this, usually involving either amplifying or stripping the sync signal, but I’m still not 100% sure why this is happening to some SMS systems. I’ll soon have an SMS page dedicated solely to fixing SMS issues (as well as one showing the RGB bypass), but installing this bypass board has fixed most of the issues in every SMS I’ve tried (you still get some interference, but it’s MUCH better).
What exactly is required for this bypass?
Here’s a quick rundown of how this bypass is performed:
Determine your sync requirements: Some people’s setups might benefit from getting sync a bit differently then normal Genesis systems. I’d consider this first, just so you can plan your installation accordingly.
RGB cable: These RGB bypass boards contain all of the components needed to output a correct RGBs signal. If you’re using an RGB SCART cable that already has resistors and capacitors in them, you can remove them from the board, as they won’t be needed.
Find a mounting location for the bypass board: On SMS and model 1 Genesis systems, the RF module location is perfect. In other models, you’ll have to find a safe place to mount it, but as long as it’s covered in non-conductive material (heat-shrink tubing, etc), you can put it anywhere and just run the 5v & ground wires to it.
Pull RGBs directly from the video chip: This bypass starts by getting RGBs from the video chip, before it’s amplified and sent to the multi-out. This can be done on every model of the Genesis, however you’ll have look up the RGBs pins on the specific chip for your console. I suggest checking console5.com, as well as Googling.
Determining your output connector: I prefer to install a Genesis model 2 multi-out into my Genesis 1 systems; This allows me to connect stereo audio to the multi-out, use Genesis 2 RGB cables and makes 32x compatibility a bit easier. It also makes the mod completely reversible (assuming you didn’t lift the RGBs pins), as nothing needs to be cut. Here’s one example of a 9-pin DIN connector that’s compatible:
If you’re using a Genesis 2, 3 or CDX, or simply prefer to use the existing Genesis 1 / SMS multi-out, you’ll need to sever the connections between the multi-out and the existing RGBs signal. This is most likely irreversible and should be done with caution.
Determine your sync requirements:
I’ll try to spare you a long, technical explanation and just say this: Genesis sync is weird. There are many scenarios where the Genesis’ csync signal is incompatible with some RGB monitors (the XM29, etc), or upscalers. If your setup already works fine, or has a sync stripper in the chain, I suggest just using sync as described in this guide. That being said, if you’ve had any issues with csync from an unmodified Genesis, or are using components in your setup that require csync from the console (many switches, etc), then it might be best to install a sync stripper internally. Basically, just follow the guide below, however take csync from the video chip and run that through a sync stripper, instead of the bypass board. Then (obviously), wire csync output from the sync stripper, instead of the bypass board. DIY instructions are here.
Testing your RGB cable:
If you’re using a custom output connector, skip this section and simply use an RGB cable with no components in it for the proper signal. If you’re using a stock Genesis cable or a 32x, you must remove certain components from this board!!! Please allow me to explain:
Video equipment is designed to receive a very specific signal. Some consoles generate this signal all on the motherboard and the cable is just two connectors with wires between them. With some consoles (Genesis, SNES, etc) manufacturers decided that some components should be on the motherboard and others in the cable. The bypass board has all the components built-in, so basically, whatever’s in the cable needs to be removed from the board.
If you’re using an RGB SCART cable made to Genesis spec’s, it already has components installed inside of it. Most cables have 75 ohm resistors in the console connector and capacitors in the SCART head. To double check, open the SCART head to see if the RGBs pins (15, 11, 7, 20) have capacitors. If so, you can remove them from the bypass board (shown below):
Then use a multimeter to test from the input side of the capacitors to the pins on the console end of the cable. If you get a tone, that means there’s no resistor there at all. If you get no tone, you should see approximately 75 ohms of resistance on your multimeter. My cable had capacitors on all RGBs pins, but only resistors on RGB, not sync, so I only removed the RGB resistors from the bypass board. Click on each of the pictures below for a full-sized view and see below for info on the bypass board:
Once you’ve determined which components you don’t need, you can remove them from the RGB bypass board. For RGB connections, if you don’t need either resistors or capacitors, it might be easier to just break off the capacitors and solder directly to the outputs of the THS7314 chip. For sync, or if you only need to remove certain connectors, make sure to bridge the connections on the board, otherwise the signal won’t get to the output pads (click for full-sized):
Here’s a closeup of a board that only needed the resistors removed. You can see how after removing the resistors, I simply dragged solder across the pins, bridging the connection:
As an FYI, if your image is too bright or too dark after performing this mod, you probably made a mistake in this section.
Summary / Tips:
This guide is filled with ominous warnings about all the potential negative things that this bypass can do. I added those to make sure I wasn’t misleading anyone into thinking this is a “necessary” mod, like adding the RGB amp in an N64. While this mod may fix issues for many people, it’s really just a preference…one that I absolutely love and prefer to use on my systems. It’s totally up to you if you’d like to try it as well, but I’m extremely happy I did.
Performing the mod:
If you’ve decided this mod is something you’d like to try, here’s everything you’d need and all the steps involved:
If you’re done, please head back to the main Genesis page. If you’d like info on mods for other systems, head to the Getting RGB From Each System page or check out the main page for more retro-awesomeness.