Re: [stella] composite video modification doesn't quite work

Subject: Re: [stella] composite video modification doesn't quite work
From: Piero Cavina <p.cavina@xxxxxxxxxxxxx>
Date: Wed, 24 Sep 1997 09:02:08 +0200 (MET DST)
At 15.15 22/09/97 -0400, you wrote:
>On 22 Sep 1997, Richard Kennehan at Cosmo02PO wrote:
>> I have added composite output to my Atari 2600, following the directions
of the
>> Atari FAQ,
>> but certain games have colors that are screwed up, such as Pitfall II,
>> Laserblast, etc.
>> Has anyone else had this problem? 
>Yep, I've had the same problem.  Even when I fiddled with the pot through
>the small hole in the bottom of the 2600, many games were still screwed
>up.  I've noticed when I change the pot though that many colors will
>change, but some don't change at all. Anybody have any suggestions?

Probably you're lucky... I had the screwed colors problem, and I found the
way to solve it!
It was a luminance problem (not color) and it made a lot of games unplayable
(thought at a first look they didn't seem so bad): in practice, the scale of
luminances was screwed and what had to be brighter was darker instead...
So, if you've the same troubles, here's my advice:

- the internal color pot won't help
- there were many revisions of the 2600 PBC, then it's not obvious which are
the good points where to take the signals from. But 1) a very helpful
document has been put on the net some months ago (don't have it here now,
maybe it was by John Dondzilla) 2) anyway you can find the signals with some
experimentation: I've kept the TV on and tried many points on the PCB until
I found the good ones (NO RESPONSABILITY TAKEN... :)
- even when you've found the signals (3xLuma + Chroma + Sync), you can
experience the screwed-luminance problem as above. Here's how I solved it:
the culprit was one of the signals, that was too strong! I've simply sent
the signal throught one of those little pots (10k I think) and turned it
until the picture looked good enough.
As a reference picture, it is very helpful that color-demo program that
Echkard sent to the list some time ago.
Just turn the pot until you get a smooth scale from dark to bright colors.

Hope i've been "bright" enough... :)




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