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!
What model Genesis / Mega Drive is a bypass recommended on?:
This is a tough decision. Installing a bypass will (in almost all cases) permanently disable composite video, leaving you only RGB. Also, with projects like the MiSTer and Analogue’s Mega Sg console, people chasing the highest quality signals no longer need to modify original consoles. It might be better for your setup/collection to recap your original Genesis console and preserve it as-is, then use an FPGA solution for gaming. That said…
All Genesis consoles will absolutely benefit from a full audio and video bypass. Model 1 Genesis consoles will have a big upgrade in video quality and while the audio is already excellent, you’ll have a slightly quieter noise floor if you bypass that too. Model 2 and 3’s generally have decent video, but not good (or just mono) audio. As a result, if you plan on modding original hardware, I strongly recommend the Sega Triple Bypass board, as it handles both audio and video.
As an FYI, simply lifting the subcarrier pin from the VDP will show a noticeable RGB video improvement in most revision Genesis 1’s, while sacrificing composite video. It’s not as good as a full bypass, but is certainly a much easier start to getting better video quality.
Why perform an RGB-bypass (or Triple Bypass)?
Jailbar fix: As shown in the picture above, performing this bypass will remove analog video jailbars from the Genesis’ output image. All analog video console will always have some noise on the signal and the Genesis / Mega Drive are some of the worst of the bunch. Still, as far as jailbars go, a bypass will fix most.
Moving the signals off the board: All Genesis / Mega Drive consoles have motherboards that seem to be much “noisier” than most other consoles…both literally and figuratively. Just tapping the audio and video signals from their sources and moving them off the motherboard seems to be a great improvement to the signals. Also, the circuits and components used in the triple bypass will be either equal to or better than what’s found on the board, while also offering more options: Audiophiles can choose between filtered and unfiltered sound and a low-pass filter can be toggled on the video output.
What exactly is required for this bypass?
Isolate RGB directly from the video chip: This bypass starts by getting RGB 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. Also, I suggest soldering to the VDP’s sync pin, but not lifting it, as some model Genesis consoles require the pin for the Z80 to run. Lastly, if you lift the RGB pins, you’ll need to replace the pullup circuit: https://www.retrorgb.com/introducing-the-sega-triple-bypass.html
Determining your RGB Cable & output connector: I prefer to always use a Genesis 2 RGB SCART cable and 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:
Panel-mount: https://www.digikey.com/product-detail/en/MD-90SN/CP-2590-ND/352878
Surface-mount: https://www.digikey.com/product-detail/en/cui-inc/MD-90SM/CP-2290-ND/145323
Breakout PCB:
https://oshpark.com/shared_projects/37rGIZ8P
https://github.com/db-electronics/MD-90SM-breakout-kicad
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.
Testing your RGB cable:
I always recommend that all mods done to any console result in the exact same output signal as the original console. This makes purchasing cables easier, as well as prevents future users from not knowing it’s modded and using the wrong cable. Essentially, for this mod, you’ll be connecting RGBs directly from the amp to the multi-out and utilizing the resistors and capacitors in the cable, just like a stock console.
If you’re using a custom output connector with a passthrough cable, you’ll need to add the proper components to this circuit. 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 Genesis consoles. 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:
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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.