To: [email protected] (triton9)
Subject: Re: Video sync problem?
References: 
[email protected] (triton9) writes:

> I working on a rgb encoder design using the AD724 RGB encoder chip. 
> The chip works fine except it is in black and white.  I think it has
> something to do with the color not going into sync.  I read somewhere
> that if the composite sync signal was run through a 74LS86 quad input
> OR gate, it would buffer or amp the sync signal.  The schematic was
> cut off so I don't have the full information.  Does anyone have any
> ideas.  Thanks
> 
> Sean
> [email protected]

Maybe you problem is that the HSYNC pulse width you are sending
to AD724 is not right. Or the frequency of color subcarrier crystal
is not right.

Check those. I used once AD722 (quite similar IC) and had
to make sure that the HSYNC pulse was right. In my VGA to TV
application the software could not alway guarantee exactly right 
HSYNC, so I had to use my own pulse shaping electronics. 
Look what I did at
http://www.hut.fi/Misc/Electronics/circuits/vga2tv/vga2palntsc.html


-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/