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Thread: OMG rgb scart cable pinout for megadrive...

  1. #16
    Hedgehog-in-Training Hedgehog-in-Training
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    I'd like to make an RGB scart cable for MD1 but using CSYNC instead of over Composite. It will be going into a 4:3 CRT so don't need to worry about 16:9 switching. Could someone provide me with a schematic please?

    When I search, I either find "sync over composite" ones or conflicting info on resistor and capacitor values. e.g. either 75ohm & 220uf on the RGB or jus the 75ohm. Plus not sure what needs to be on the CSYNC pin but I understand the MD outputs +5V TTL on it so can't be used directly.

    I assume that if you make this sort of the cable you don't need to do any internal "sync mod" on the Mega Drive? I'm not looking for uber quality, just something better than the usual RGB cables on eBay. I could buy one, but I have all the components already and soldering skills so why spend 30!
    Last edited by itsamemario; 10-17-2022 at 04:56 PM.

  2. #17
    Hedgehog-in-Training Hedgehog-in-TrainingWildside Expert majinga's Avatar
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    There isn't a standard value for the csync.
    Most time a 220uF + a resistor is enough. But you have to find the correct value for your TV.
    With a modded MD is more complicated, because is not easy to find a value for both the video mode.

    Plus, on the MD the csync is connected on the wrong pin of the encoder.
    So, you have to check if you can use it directly with your TV.
    Otherwise you need a buffer.

  3. #18
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    Quote Originally Posted by itsamemario View Post

    When I search, I either find "sync over composite" ones or conflicting info on resistor and capacitor values. e.g. either 75ohm & 220uf on the RGB or jus the 75ohm. Plus not sure what needs to be on the CSYNC pin but I understand the MD outputs +5V TTL on it so can't be used directly.
    Yes, the digital Csync signal output cannot be used directly.

    Back in 2015 I saw some tests made with an oscilloscope and the conclusion was that it was necessary to reduce the signal level with a 470 ohm resistor (best installed at console end) and use a 220uF capacitor to remove DC offset.

    I made a cable myself and put the resistor inside the Din plug and the capacitor on the other side (inside the scart plug) and it worked.

  4. #19
    The legendary gargoyle Road Rasher Firebrandx's Avatar
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    Funnily enough, you can get sync on luma by removing the subcarrier signal inside the console (turns composite video to a grayscale luma output). Sync on luma is arguably the best sync (as long as you're not using Extron Crosspoints) because it's a noise-free standard that doesn't require determining resistor values and tolerance swings with upscalers.

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