[Coco] Coco compatible monitors...

[Michael Graham]

I'm actually using an IBM PCjr monitor for my CoCo3. I just installed a
switch that allows me to bypass the internal digital color generation
circuitry, and I wired in a ribbon cable with the proper plug to the
analog side of the circuitry. It worked without modifying the signals,
for me, but I had to mess with the saturation level adjustment on the
monitor a bit (which, surprisingly, did not seem to affect the PCjr
video signal at all).

I got the idea from this guide here:
http://www.mikesarcade.com/cgi-bin/spies.cgi?action=url&type=conv&page=SamtronCGAtoArcade.txt

Only difference with the PCjr monitor was that the colors were assigned
to different pins on the 74ls38. And I didn't need the inverter chip or
sync splitter since the CoCo3 already outputs the proper signals there.
And, of course, I had to figure out where to input the sync signals
myself, since the PCjr monitor used different connectors internally. Oh,
and lastly, the PCjr monitor has a built-in speaker, so I was able to
hook up the CoCo3's audio output to that.

I figure there are probably a lot of CGA or EGA monitors that use the
same kind of circuitry as these monitors, and could probably be bypassed
for an analog signal in the same way.

-Michael


On Fri, 2011-07-01 at 12:07 -0400, Robert Gault wrote:
> Mark Ormond wrote:
> > I've got some NEC Accusync LCD 71Vs in my shop. And playing with groovymame I found that they will sync to 15 and 24k signals,so I hooked one up to my Amigas, but they only display NTSC correctly, pal screens get cut off (I think the monitor only does 240 lines @ 15k). Do you think these will work with the Coco3 with a cable adapter?
> > .7v p2p on the input voltages, what does the 3 output?
> >
> > Just a thought.
> >
> > (As a note, the tech specs on this monitor say Synchronization Range - Vertical 56 - 75 kHz ,Horizontal 31.5 - 81.1 kHz, but this isn't correct.)
> >
> > Later,
> > dabone
> >
> >
> 
> The Coco3 service manual lists 0.8-2.0v +-0.2 at 75ohm NTSC
>                                 0.6-1.8v +-0.2 at 75ohm PAL
> 
> For my monitor, I found the signal too hot (required 0.3-1.0v at 75ohm) so I 
> placed resistors in series with the RGB output (about 1ohm each line I think) to 
> reduce the signal. Checked with a scope.
> 
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