Re: pin driver difference between early/later VIC-II?

On Mon, Mar 8, 2021 at 11:52 PM Peter Rittwage <peter_at_rittwage.com> wrote:
>
> This effect can be mostly eliminated by converting to Y/C video output.
>
> I find the 6567R56A and the original 326298 board video output looks really
> good with a couple simple mods.
>
> First, I put a 25-33ohm resistor between the left side of R9 and GND (left
> side of R11) which gets you about the right signal levels on the Luma line,
> as it's much too high normally on it's own.

that's quite some load to Q4. The proper way to reduce the signal
would be increasing R9, this makes a voltage partition with the luma
input which is usually 75ohms.
By the way, R9 from the schematic seems to be 7.5 ohms? I need to
check on the actual board. If it's indeed so low, I would try a 75
ohms R9 instead.

>
> Next, lift the right side of R10 to convert the composite output to
> Chroma-only. It does clear up the signal just a little (less color moire
> interference on the edges in Y/C mode) than using the full composite signal
> as your Chroma.
>
I've seen this mod already, but I don't feel like modifying the pinout
of the 5 pins connector.
I asked if someone knows if it's an internal delay problem on the R56A
(which is basically unfixable) or if it's a difference on drive
levels/current out of the chroma/luma pins of
the R56A which would be easily fixable with a few component changes
(as long as one understands first the problem, since I'm not going to
play with values unless I can simulate it
on, say, LTspice first).

> Connect the Luma and Chroma to the Y and C inputs on a compatible monitor
> and it will look at least as good as the 250407 board.

this is interesting, if the color phase gets corrected by removing the
"mixing" to composite, it's likely to be a drive issue, but so fare I
couldn't figure out a good way to understand
what's the difference. Maybe if I can make the C64 generate some
simple patterns like crosshatch and/or color bars it would get easier.
Does anyone know if there're programs that output video test patterns
from the C64?
Thanks


Frank IZ8DWF