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Thread: Tech Rant: Fix the VA0 32X's fugly composite video

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    Outrunner Eep386's Avatar
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    Default Tech Rant: Fix the NTSC VA0 32X's fugly composite video

    Myth: The 32X cleans up composite video.
    Reality: The 32X makes the composite video, regardless of encoder that may be present in the system, look little better than a KA2195D. It's dark, blurry, pixellated and oftentimes somewhat dull colored (though thankfully not off-tint like the KA2195D, it lacks that encoder's distinct 'bend' toward green). So how can we fix this ugliness?

    Fortunately, it's fairly easy to get a significantly less disgusting picture out of the device. Well, at least for the VA0 revision. I don't have a VA1 model handy to see if this will work as-is on it though, so this rant will focus on the VA0 primarily.

    Also this is for the NTSC version. PAL 32X's conform to a different subcarrier frequency so different component values will be required.

    What you do, after cracking open your 32X (no, not with a claw hammer - the 32X isn't that bad :P) and removing the RF shield, you take a look at inductor L5 and capacitor C74. Change L5 to a 47uH inductor and C74 to a 47pF capacitor. The 32X uses 0603 (1608 metric) sized parts except for the inductors, which are through-hole. This will set the Luma notch filter to match the JVC X'eye's, slightly reducing the blur. (More on this later.)

    Next, we'll want to replace R45 and R47 with 330 ohm resistors. This will make the picture appear a fair bit brighter and even a little bit more saturated (not quite as dull colored as before). We then add a 680 ohm ~ 1K ohm resistor to the empty pad at R48 (Sega *really* should have fitted a resistor here, but they didn't in a lame-ass attempt to eliminate cross-color at the expense of horizontal resolution). This will significantly clean up the pixellation; however depending on the resistor you apply the cross-color may become somewhat more noticeable. It's least noticeable with 1K, though it looks more pixellated the higher the impedance. On my TV, 1K looks fairly good in both respects, but YMMV. You may have to experiment a little to see which impedance value looks the best to you on your TV.

    Finally, we'll want to do something about that damn fish-tank like blur. Fixing the Luma notch filter helped a little bit, but after replacing R45 and R47 we'll want to go a little further. We turn our attention to C75. Sega used a quite aggressive 56pF cap here, put a 36~40pF cap in its place. I used a 33pF, which might be a little bit too low as I begin to see some very faint 'ghosting' artifacts to the right of certain graphics. You may have to use a higher value than 36pF if you used a lower-valued resistor than 1K on R48.

    If all goes well, enjoy your now considerably less pixellated, less blurry and brighter picture!

    I'll try to get some pics up ASAP. I don't have a working SD card reader ATM so I'll have to get one installed...
    Last edited by Eep386; 05-27-2019 at 12:49 AM. Reason: Never the Same Color

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    This might be irrelevant to composite encoding as well as to the Megadrive and 32x video output, but are you sure the video output isn't bad simply because the output filter caps are spent?

    On my Saturn, recapping the system made a very visible difference in video output (the colours were significantly less washed out).

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    Outrunner Eep386's Avatar
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    Sega left off a crucial resistor that was needed to prevent excessive pixellation. In the schematics of the 32X's technical manual, this resistor (R48) was listed but marked 'DO NOT USE'. Putting a 1K here makes the video much less pixellated.

    In any case I'm fairly sure dried out caps wouldn't generate pixellation. Noise on the screen, maybe, but not pixellation. I'll recap this thing later once I get more caps.

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    Video Game Modder Outrunner segasonicfan's Avatar
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    Excellent post and guide as always! Could we hope for pictures at some point?
    Thanks for documenting this.

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