can s-video output be "tweaked"?

Jeremy Wilkins jeb at
Wed Nov 22 10:45:35 PST 2006


Don't know if it helps, I used to use a homemade VGA to Scart lead,
and got pretty good quality out of it. below are the mode lines I used
for it. I believe the ForceMinDotClock option is vital because by
default the ati driver won't sync low enough.


Section "Device"
        Identifier      "ATI Technologies, Inc. RV280 [Radeon 9200 SE]"
        Driver          "ati"
        Option          "ForceMinDotClock"      "15MHz"

Section "Monitor"
        Identifier      "TV"
        HorizSync       15-30
        VertRefresh     50
#       TV out modeline for 720x576
        ModeLine        "720x576PAL" 15.125 720 770 842 968 576 579
607 625 Composite Interlace
#       TV out modeline for 720x540
#       ModeLine        "720x540PAL" 15.101 720 770 842 968 540 565
570 624 Composite Interlace

Section "Screen"
        Identifier      "Default Screen"
        Device          "ATI Technologies, Inc. RV280 [Radeon 9200 SE]"
        Monitor         "TV"
        DefaultDepth    24
        SubSection "Display"
                Depth           1
                Modes           "720x576PAL"
        SubSection "Display"
                Depth           4
                Modes           "720x576PAL"
        SubSection "Display"
                Depth           8
                Modes           "720x576PAL"
        SubSection "Display"
                Depth           15
                Modes           "720x576PAL"
        SubSection "Display"
                Depth           16
                Modes           "720x576PAL"
        SubSection "Display"
                Depth           24
                Modes           "720x576PAL"

On 11/22/06, José Oliver Segura <primijos at> wrote:
>        Hi all, (hope not to be off-topic)
>        I'm trying to configure s-video output from my laptop (Acer
> travelmate 240, ATI Radeon Mobility 7500) to my TV (Sony  trinitron KV
> 32'') under Linux (Fedora Core 6).
>        I'm able to see the desktop in the TV (just used atitvout to
> activate s-video output), but I think the picture is not as good as it
> could get: image doesn't feet 100% of the screen, is a little
> displaced towards the left and, at the top, the line is not completely
> straight, is a little bit curved as it gets next to the left border.
> Also, when viewing some channels on dvb-t, I can see little
> dots/slashes in this same place (the curved edge on the top right).
> Picture also presents some little horizontal lines but only at
> "objects/shapes limits" (don't know how to explain it better). I've
> tried with "radeon" driver and "vesa" driver (both Xorg, I've not
> tested ATI propietary drivers)
>        I've tried the same s-video cable with another laptop (hp
> nc8000 + windows) and it works ok (image size fits screen, no
> horizontal lines at shapes edges).
>       I've been looking around to see wether change some parameters in
> xorg.conf file would end up with a better picture, but nothing has
> worked (mainly, tested different modelines in xorg.conf), so I'm
> starting to think that maybe I have some *big* misunderstanding of how
> s-video output works, and maybe none of the parameters in xorg.conf
> files affect that? maybe, as s-video is, in someway, "dedicated" to
> TVs, everything is hardwired in the chip?
>        Is it that way or is just that, maybe, I'm not getting the
> right modelines/head configuration, whatever?
>        Sorry about not posting xorg.conf/logs now, I'm at office and
> have no access to my home's laptop, but since this is a question
> related with general s-video tweaking (before going deep into details,
> if it can be done), maybe is not necessary. If I get any "yes, it can
> be configured!" answer, I'll be happy to continue the thread, posting
> xorg.conf files :)
>        In parallel to that, I'm trying also the vga<->scart option:
> just bought a vga<->scart cable and plugged it from the laptop to AV/1
> in the TV, but that's worse: no picture at all :-/ Maybe this case is
> more sensible to modelines and TV refuses to show any signal that
> doesn't fit exactly in their refresh/sync range? (I have not been able
> to make this setup work undre windows, so I'm starting to blame the
> vga<->scart cable, althoug the fact that a "crt" is attached to vga is
> detected in bot: windows and linux)
>        thanks a lot for any hit, have a good day!
>        Jose
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