This is an old post, preserved for reference.
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Following on from the Atari 400 composite video conversion I did recently, I was asked to do an S-Video version.
TFW8b.com video buffer boards, one for the luminance signal, and one for the chrominance. The ground and 5V lines are commoned, red and black for power and white for audio as usual. Yellow is used for luminance, and green for chrominance.
48K RAM board in the background.
the composite mod.