[Coco] Composite Video Mod for CoCo1

[Daniel Campos]

Hello,

Since I got the Color64 (Coco1 clone) his image, even already having a
composite video output, have always disturbed me with a crap image
compared to other CoCo machines. So I began to try to correct that and
removed the entire transcoder analog pcb that came with the computer
and used the schematic bellow to try to have a better composite
output:

http://www.victortrucco.com/Diversos/MC1000/SaidaAV.JPG

The schematic above is largelly based on the driver for color
composite video that is showed on the 6847 datasheet. After build the
mod, image is great on text mode, sharp and crispy, the problem begans
when I got to the graphics mode using artifacting. For example, on
Outhouse, the initial screen should be red, but appears with a very
pink saturated color, it's impossible to read. Other games, like
Draconian and Galagon got very saturated too.

My question is, someone here have done any of the scematics bellow and
worked fine on a LCD monitor with composite video ?

http://www.retrocomputers.eu/wiki/index.php/Tandy_TRS-80_Color_Computer_(CoCo)_Composite_Video_Mod

http://sd2cx1.webring.org/l/rd?ring=coco;id=1;url=http%3A%2F%2Fwebspace%2Ewebring%2Ecom%2Fpeople%2Fvt%2Ftheother_bob%2Fcoco_page%2Fccprojects%2Ehtm

Any suggestion would be higly appreciated. :)

Thanks,
Daniel