[Coco] Quick question re: RGB -> VGA

[Dave Philipsen]

Has anyone on the list successfully connected a CoCo 3 to a GBS-8200 converter? This is a cheap Chinese converter you can buy on eBay for under 20 bucks. I'm experimenting with one now but with the lack of any good documentation I'm having some problems.  From some posts I've read in some forums it's starting to look like the GBS-8200 wants composite sync when you're working with CGA-frequency signals.

Right now I'm getting a choppy signal that won't stay locked in. I can see the sign on message intermittently and the color is right but the sync isn't working yet. At first I thought it was sync polarity so I cobbled up a little circuit with a couple of 2N2222s to invert the sync. The 'scope shows nice inverted signals but the converter still doesn't lock to the signal.  I'm guessing the next step should be to try using a NOR gate to combine the HS and VS to make it composite.

Dave