🚀 go-pugleaf

In article <1990Feb20.020108.595@uncecs.edu> dev@uncecs.edu (Dev Palmer) writes:
>
>I hooked the Xerox video connector (hsync, vsync, video, ground) to the RGB
>connector on the CGA card (hsync, vsync, RED, ground), and actually got some
>output!  The only problem is that there is no color differentiation as there 
>appears to be on the composite monitor.
>
>My question is: can you combine the R, G, B, and possibly intensity signal from
>the CGA card into some video that the Xerox can detect?
>
	It sounds as if you have a TTL monitor input (i.e. the video
is received, inside the monitor, by a TTL gate).  This will not detect
intermediate voltages, only logic HIGH or LOW, and will not spit out 
any shades-of-gray signal to the monitor.  
	Trace the wires from the video input (this signal path is
typically, on an ANALOG monitor, a two-transistor cascode amplifier).
If you find a TTL gate, consider rewiring the video to the gate's 
output point (you'll have to cut the printed circuit wiring to do this).
If you find an interface chip (like SN75451) you may have to build your
own amplifier.  If you find a two-transistor cascode amplifier, then
I guessed wrong.
	The amplifier will need circa 30-80V output to drive the
CRT from dark to full brightness, and about 20 MHz bandwidth.
Two transistors, in a cascode, works well.
	Conventionally, the GREEN output is used for black/white display
from an RGB color source.

I am known for my brilliance,                   John Whitmore
 by those who do not know me well.