[Coco] Will this build-your-own s-video board work for CoCo 3?

[Steven Hirsch]

On Tue, 8 Mar 2011, Steve Bjork wrote:

> A simple Google search came up with this from CoCo3.com...
>
> In the case of the Amiga 1084, it requires combined negative sync in
> analog RGB mode, so you need to take the separate positive H and V sync
> from the CoCo and feed them into the inputs of a a NOR gate a 74LS02
> has four such on it, and use the output of that NOR gate to provide
> sync to the Commodore monitor.

Here's a nice writeup with several schematics for an H / V --> H+V 
converter:

http://www.epanorama.net/circuits/vga2rgbs.html

I threw together the version for "TTL level sync", fed that into an 
el-cheapo Chinese CGA to VGA board (< $40 on eBay) and was able to get 
decent display of CoCo 3 video on a Dell LCD monitor.

That said, Roy's unit does a bit better job at eliminating fringing 
effects.  I tried building a low pass filter per his recommendation, but 
it did not seem to help - probably because the input impedence of my 
converter is different from his.

Steve


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