Path: utzoo!mnetor!ghp!jim
From: jim@ghp.UUCP (Jim Stewart)
Newsgroups: sci.electronics
Subject: Composite Colour Signal (help my sanity)
Keywords: NTSC
Message-ID: <507@ghp.UUCP>
Date: 19 Feb 90 15:52:28 GMT
Lines: 31

I have an old CGA that I am trying to get working with the composite
input to my colour TV.  Before everybody says "why", it started as
a project to get a cheap machine going for my kids, age 8 and 5.  If
they destroyed it it wouldn't be a big loss.  BUT!  Now unfortunately
it has become a matter of my sanity.  I might even spend the money
to buy a better monitor, etc., but first I going to get the #@%&$%!
thing working.

The current system works fine, on a monochrome composite monitor.
It also works in black and white through the video input on the colour
TV (i.e., I display a game I know is in colour, but I only get grey
and white).  I have looked at the composite output from the board.
I can see the colour burst, I can see the colour modulation, I think
I have the right levels, the colour burst frequency is in the right
range (pretty lousy accuracy from a scope).  I talked to an engineer
that used to manufacture televisions.  He said to be sure of several
parameters, but as I pressed he didn't leave me comfortable.

What are the critical details of NTSC with respect to colour?  I can
post the parameters I measured if that helps.  Maybe my CGA clone
was never intended to do composite colour, the RCA phono was only
there for good looks, but I need to know why before I can let it go.

I've spent about a month on this so far, so any help will be appreciated.

tnx

-- 
Jim Stewart, VE3SRJ
UUCP:  jim%ghp@mnetor.uucp
BELL:  (416)862-0430