[Coco] CoCo SDC board arrived and RGB to VGA converters

[Steven Hirsch]

On Fri, 7 Feb 2014, Gene Heskett wrote:

>> Speaking of CoCo 3 output to VGA converters, has anyone try this one the
>> SainSmart GBS-8220 RGB/CGA/EGA/YUV to VGA Arcade HD Video Converter
>> Board?  It runs about $30 and here is the link:
>> http://www.amazon.com/SainSmart-GBS-8220-Arcade-Video-Converter/dp/B0051
>> SLJAG

> I have one, had to cobble up a composite sync signal to make it work, video
> gain is a bit low.  Roy's latest version has better gain & just slightly
> sharper.

> It has several inputs, but the only way I found to get a stable pix out of
> it was to use the molex header posts, and cobble up an inverted polarity
> composite sync.

I have one of these, purchased for use with my CoCo 3.  Never really 
looked very good and OS-9 80-col text was particularly smeary.

I built a sync combiner based on:

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

This circuit is very interesting in that it generates a correct composite 
output regardless of raw H/V polarity.  You can control the polarity of 
the resultant composite output by tying pin 13 of the final XOR gate low 
or high.  The GBS-8220 doesn't seem to care what polarity it sees, 
however.

The only converter + display combination that seems workable is a Wei-Ya 
CV-04 RGB --> S-Video converter driving a Dell 2001FP display.  For some 
reason I need to set the converter to PAL video in order to avoid an odd 
"swimming" effect (probably a beat frequency).

Maybe I'm just overly fussy, but none of these solutions are really as 
easy on the eyes as a CRT monitor.  All of them have some level of 
instability and artifacts of one type or another.

Steve


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