[mythtv-users] Stupid S-Video Problem Continues
Brian Wood
beww at beww.org
Thu Jun 8 14:56:31 UTC 2006
On Jun 8, 2006, at 7:56 AM, Will Constable wrote:
>
>
> Yea- my current setup is s-video via homemade cable—40 ft of cat 5
> with s-video and audio connectors at each end, running through the
> walls- I know, sounds like a recipe for disaster. But my laptop
> drives a perfect signal from one end to the other while I have this
> problem with the myth box. So I am thinking its either the card or
> the settings/driver.. I have been using nvidia instead of nv, but
> have not tried a whole lot of options for resolution on my vga
> port. I was thinking it would be good to try identical settings
> and do a clone, but I don’t know how to write xorg.conf for that—
> mine does dual screens not using xinerama. It does occur to me
> though, that the setup I have upstairs is 1024x768 on s-video and
> 1600x1200 on vga—while the monitor downstairs cant run 1600, maybe
> this setting would make the interference go away. Do you know how
> to set up xorg for clone? Also, can I set the horizsync and
> vertrefresh of my vga monitor to match what my tv uses, or might
> this cause a problem?
>
>
>
>
Some things to try:
Since you get a good signal with your laptop, try moving your TV set
next to your Myth box and connecting it up via a short S-Video cable,
if you still see the problem this will confirm that the problem is
not your home-made cable.
It is possible, almost probable, that the problem *is* your cable,
and something is different between your laptop and your Myth box, for
example your laptop probably has only one video signal, the S-Video,
and not a differing VGA floating around.
As you seem to realize, you have broken just about every rule about
video cabling :-) But this doesn't necessarily mean you won't be able
to get it to work.
It could also be something like your laptop having a different
grounding scheme, in fact it may well be more resistant to common-
mode interference because the power supply is not referenced to your
house ground, or the exact VGA rates of your laptop are just enough
different as to render the problem invisible.
Changing the resolution of the VGA signal may well help your problem,
the interference will still be there but the rate difference will be
different and thus might well cause it to move through the picture
fast enough to not be noticeable. Changing the rates of your VGA
signal will have the same effect, though setting them to be the same
as your TV may well cause an interfering bar to simply be static,
unless you can "genlock" them to a fixed phase relationship,
something beyond most PC systems.
The README included with the nVidia driver explains how to set up
clone mode, but having the same image on both screens is not the same
as having the same video parameters.
In short, your cabling arrangement is in all probability the source
of your problems. Rules and standards exist for a reason. The type of
interference you are having is very sensitive to the precise
frequencies involved, if they are close enough to each other (or
their harmonics or beat products are) then you will see visible
artifacts, if they are far enough away from each other the products
will move through the picture fast enough to not be a bother, but
they are still there, and could be measured with the right gear.
Differences on the order of fractions of a percent of the sync rates
can make the difference, and these are well within the tolerances of
modern video cards. Simply trying another "identical" card might make
a difference.
You could always use that cat-5 for what it was meant for - ethernet,
and just put a MediaMVP at your set for about the same cost as a new
video card :-)
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