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: Tue, 23 Sep 1997 17:59:19 +0100
>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?

I had a similiar problem too, and I've successfuly solved 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 so that different lum values gave the
same luminance, or 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 have been many revisions of the 2600 PBC, then it's not obvious
which are the good points where to get 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 good points with 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, it was too strong!
I've simply sent it through 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 (bravo!) :-)

Just turn the pot until you get the correct scale from dark to bright.

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


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