[Coco] Yellow tinge

[Gene Heskett]

On Wednesday 13 September 2017 20:31:59 Zippster wrote:

> Really close Gene.  It is indeed related to color burst.
>
> The “artifact” circuit in the CoCo2, which uses a 555 timer IC circuit
> to pull on one of the color phases (causing the 1372 to generate a
> pseudo color burst) gets out of tune, and pulls the phase lower for
> too long.
>
> This causes the yellow bar on the left.  I’ve also seen a bad diode in
> this circuit constantly drag the phase lower than it should be,
> causing a yellowish tint over the entire screen.
>
> - Ed
>
There is that possibility too.  I was offering a SWAG, as I have not 
personally encountered the timer problem myself.

> > On Sep 13, 2017, at 6:50 PM, Gene Heskett <gheskett at shentel.net>
> > wrote:
> >
> > On Wednesday 13 September 2017 07:06:40 Carlos Camacho wrote:
> >> I have two CoCo 2 for sale on eBay and a customer pointed out one
> >> of them has a yellow tinge running vertically on the left side. You
> >> can't see it on the BASIC screen. You can see it with a white
> >> background screen like Canyon Climber. I recall some video
> >> composite boards have this issue, but haven't heard of it with
> >> regular RF out. It's not the monitor as my other CoCo for sale
> >> doesn't have it.
> >>
> >> So what is the yellow bar and how to remove it?
> >
> > As an old ntsc broadcast engineer, I'd expect its the color burst,
> > which is sent late in the horizontal retrace time, and is nearly a
> > yellow, and which would show up on the left side of the screen, and
> > a monitor that didn't do a good enough job of blanking the video
> > during this time will generally show it.  Whether you see it or not
> > will be quite dependent on the monitor being used.
> >
> >> Thanks,
> >>
> >> Carlos
> >
> > Cheers, Gene Heskett
> > --
> > "There are four boxes to be used in defense of liberty:
> > soap, ballot, jury, and ammo. Please use in that order."
> > -Ed Howdershelt (Author)
> > Genes Web page <http://geneslinuxbox.net:6309/gene>
> >
> > --
> > Coco mailing list
> > Coco at maltedmedia.com
> > https://pairlist5.pair.net/mailman/listinfo/coco


Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>