Last night I hooked up my 2600 and tried to "prop up" the Pitfall II
cart, as described here earlier. Guess what? It *worked*! Thank you
guys. Still I wonder if there's a way to get it working again without
needing to be propped.
Anyway, I also tried to prop the Mangia cart, and this one didn't work.
So I think it's really the bits got rotten here. But since this is not
such a great game (and it's on a wanted list of someone who even is
interested to give me something for it), this is less important. For
propping, I used a Ms.Pac-Man cart. Of course, afterwards I wanted to
know if this one still worked, and put it in, and came across something
strange, which I think has nothing to do with the propping:
Some of my carts seem to display a sort of interference in the black
part of the picture (and also in other parts, but not so good visible).
You can see it at least if you hook up the VCS to a VCR and on to an
Amiga 1081 monitor, but maybe you also can see it on a TV.
The pattern of the interference will be visible if you turn the
brightness control up very high, so that the black appears as grey.
There are some stripes appearing, which seem to be the processor cycles,
since they're all 3 pixels wide. Still, they only appear at some carts,
and not at the whole screen. Some examples:
-Ms. Pac-Man: They appear below the displaying part of the screen.
-Q*bert: They seem to be in the whole screen here.
-Mario Bros.: On the title screen, they only appear at scanlines where
something's displayed. At the other scanlines, they don't appear.
-Moon Patrol, Smurf, Carnival... There are no interferences here.
Now the question is how these interferences come together, and why they
only appear at some carts. Does it have to do with bank-switching, or
with a special way the kernal is written? Does the interference
disappear why the processor waits for a WSYNC?
Only interested in it... Has anyone else come across these
interferences?
With love (and about 60 visible vertical stripes per scanline)
Kurt Woloch
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