S-Video/Composite Driver idea

the_crayon_king · September 24, 2022

The overall idea is that this should work to take the Y/C signals before they are mixed into RF; then amplify Y/C and mix CV to TV levels.

As far as I know most consoles have an area that does this. Figuring out where and the voltage may take me a bit.

Notes:

If a console doesn't have a Y/C mixing spot then it won't work with this (NES comes to mind).

Will not take inputs below 0V (so do not feed inputs through capacitors).

I have taken zero IRL measurements to confirm this will work or not (made this on a whim).

This needs Luma (with sync) and Chroma to work. NOT composite.

This outputs S-Video and Composite.

Sized about 1.1 inch by 1.4 inch.

You will need at a bare minimum a multimeter to use this; ideally you would want a O-scope.

I may have to add a DC offset to this design so that is TBD.

Not made to deal with Chroma delay (for example the Ataris where this is an issue).

How to use:

Remove RF modulator?,. separate Chroma and audio from the RF mixing area (this will have to be outlined per console).

Luma and Sync will be the input going to "YI"

Chroma (and burst if applicable) will be the input going to "CI"

5V and Ground should be easy to find.

With a multimeter/ohmmeter. Set the pot to 100Ohms or so (test between the adjacent "TP"s on the bottom of the board.

Hopefully have a white screen or otherwise a screen that has white on it.

Adjust the "Y trim" potentiometer (toward higher ohms) until the white area appears white on your TV.

Turn the power to the console off and measure the Ohms of the Y-trim potentiometer.

Mirror the "Y trim" Ohm value to the "C trim" pot (measure C's test points).

Power on and the make minor adjustments to C until satisfied.

If you have an oscilloscope adjust Y-trim with a white screen until reaching 2V p-p on the output "Y" or 1V p-p if terminated.

After I take measurements of a few consoles RF mixing spots I will know if or how much this needs modified.

Anyway, this was just to gauge potential interest and see if anyone had any input.

Edited September 24, 2022 by the_crayon_king

Recommended Posts