[Coco] Yellow tinge

[Gene Heskett]

On Wednesday 13 September 2017 21:31:35 Zippster wrote:

> Oh sure.  I only know with such certainty because I’ve encountered
> it several times now.  It seems to be a fairly common problem with
> older CoCo2’s at this point.
>
> SWAG, I actually had to look that up…   :)
>
> - Ed

Darn, Ed, giving my age away, again. I think it was in '58 or '59 when I 
heard it the first time while helping build the tv cameras that were on 
the Navy's Trieste when it went to the bottom of the mohole.  Sorta 
seemed like a good one to remember at the time.  Gives a little class 
and credibility to a common Wild Assed Guess, don't you think?

One of the other project engineers was fond of measureing the video 
bandwidth of a proposed circuit, and if suitable for video, he would 
solemnly declare it was as "flat as a plate of pee". Weird part was, we 
were measuring a hank of common 16 gauge Packard automotive wire, while 
it was submerged in a 1000 gallon stock watering tank, filled with 200 
lbs of rock salt, filled from a small pump stuck in Mission Bay, which 
we had at the rear of our building.  Rock salt stirred in and dissolved 
in that brackish water by a 5 hp outboard motor.

Against all bets, it actually worked quite well as long as our sweeping 
gear was grounded to the stock tank.
>
> > On Sep 13, 2017, at 7:59 PM, Gene Heskett <gheskett at shentel.net>
> > wrote:
> >
> > 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.


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>