Fixing RGB Output on the Neo Geo CD

I recently bought an RGB SCART cable for the Neo Geo CD, I figured it’s all I needed to get super high quality Neo Geo CD video working with my Open Source Scan Converter (an upscaler). It didn’t work at all and I just assumed it was a faulty cable or my Neo Geo CD was busted, it still worked with S-Video and Composite so not a big deal. I somehow missed a paragraph of text on the ordering page that says the Neo Geo CD needs CSync mod in order to get a proper RGB signal.

Paragraph from https://www.retrogamingcables.co.uk

BEFORE WE GET STARTED A SMALL WARNING:

The CSync guide I was linked to didn’t end up working for me in the end and I’m not 100% sure why, I did manage to overcome this by using a different source to get a proper sync though. I’m not sure which version will work for you but I am now using Sync on Luma and it works and looks great!

The link brought me to this blog post about how to do the CSync Mod: https://www.retrorgb.com/ngcdcsync.html  I also did some cursory research on the subject and found that the OSSC needs some specific settings to make even a modded Neo Geo CD output correctly.
Specifically in “Sync Options” Menu:

  • H-PLL pre and post coast – 3
  • Hsync tolerance – 10us (or higher)

Here is a video of me being super dreadful at Samurai Spirits 3 captured with the Camlink through RGB SCART on the OSSC:


So let’s get started!

For reference here is the unmodified underside of the video/power board:

Cutting Traces:

Cut where the red lines are

I’m not a big fan of cutting traces on boards, but the RGB stuff seems genuinely broken on Neo Geo CD, even with these traces cut, the other video options will still work.

To cut the traces, simply take a hobby knife/blade and cut along the red marked lines, being careful not to cut too deep. If you have a multi-meter you should check that the lines don’t have continuity, if you don’t and you have issues later, check back on this step.

Wiring for Luma Sync:

We are going to get our Sync signal from our S-Video port, for context, S-Video has two useful pins, “Chrominance” and “Luminance + Sync”.

I’m not really an expert on video signals but from reading up and testing it out it seemed safe enough to try and it worked!

Solder the wires to the above points. Luma is the correct voltage so there is no need for a resistor here.

You should be getting a super clear picture without any issues, but if for some reason you are not, first make sure your OSSC settings are correct if that doesn’t work perhaps try the Csync method below.

Wiring for Csync:

DISCLAIMER: This method did not work 100% for me, I got signal, but very dark!

Simply solder some wire to the above points. We are getting our CSync signal from the third pin from the left on the bottom row. The voltage from this pin is 5v and the the RGB pin should be outputting 3.3v so we need to put a 470ohm resistor on between the two.

You should be able to get a signal on your OSSC, if not, first make sure your OSSC settings are correct. If it’s still not working and you have not tried the Luma method above, try that, if it isn’t working after that, I’m afraid I won’t be of much help =S

Here is a video showing you what was happening for me:

If your image is too dark, consider doing the Luma mod instead. If you happen to have any information on why this method can produce dark screens, please let me know in the comments below or on Twitter @TheShaneOBrien

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