Odd issue with LCD TV over VGA (Win vs Linux) [SOLVED]

[Shan]

I recently picked up a Westinghouse LTV-37w2 LCD HDTV to replace a small 20" LCD tv that was the primary display of a media-center box. Long story short, is after adjusting my xorg.conf file to fit the 1360*768 resolution; I get what I can only describe as refresh lines on my screen.

They look very similar to the effect you get when you film a CRT with a video camera, only theirs two; spaced evenly apart (approx 1/2 screen height apart). I've used various modeline generators to try and correct the issue, and while the modelines can effect the speed in which the lines move, they never seem to get it just right.

Thinking it might be a TV issue, I hooked the beast up to my laptop in windows (initially to try and get the edid which came out corrupted in linux, on the advice of the author of read-edid); and my laptop picked up the 1360x768@60 resolution perfectly, no "refresh" lines at all.

My problem is compounded by the discrepencies between the online manual and the one I got with my TV.

On page 33 of my manual it reads:

PC Compatible
Recommended 1360 x 768 @ 60Hz
Supported
1280 x 720 @ 60
1024 x 768 @ 60,
720 x 400
640 x 480
H=30~48KHz V=50~75Hz

whilst the online reads

PC Compatible
Recommended 1366 x 768 @ 60Hz
Supported
1280 x 1024 @ 60, 75Hz
800 x 600 @ 60, 75 Hz
1024 x 768 @ 70, 75 Hz
720 x 400 @ 70 Hz
848 x 480 @ 60Hz
640 x 480 @ 60, 75 Hz
832 x 624 @ 75Hz (MAC)

As you can see, the digital (and one would presume "updated") copy changes the reccomended setting to 1366x768@60 (the units actual naitive mode), adds several other supported settings, and leaves out what the Horizontal and Vert refresh rates are.

A line in both copies of the manual reads

Code: Select all

H/V separated (TTL) for PC; fh: 30-80 kHz, fv: 50-75 Hz

Which leads me to believe that the Horiz is actually 30-80Khz instead of 30-48Khz but I'm leery of actually trying it as I don't want to screw up my new TV until I'm sure; however in order to generate a modeline at the recomended resolution at all, I need to increase the max horizontal to around 60Khz.

For What its worth; All of this is on an nVidia GeForce 5950Ultra via VGA to VGA with the 9755-r1 drivers.

Follows is my xorg.conf file; logs upon request (because their bloody huge)

Code: Select all

hammond ~ # confcat /etc/X11/xorg.conf
Section "Module"
    Load        "dbe"
    Load        "glx"
    SubSection  "extmod"
      Option    "omit xfree86-dga"
    EndSubSection
    Load        "freetype"
EndSection
Section "Files"
    FontPath   "/usr/share/fonts/misc/"
    FontPath   "/usr/share/fonts/100dpi/"
    FontPath   "/usr/share/fonts/75dpi/"
EndSection
Section "ServerFlags"
EndSection
Section "InputDevice"
    Identifier  "Mouse1"
    Driver      "mouse"
    Option "Protocol"    "Auto"
    Option "Device"      "/dev/input/mice"
    Option "ZAxisMapping"   "4 5 6 7"
EndSection
Section "Monitor"
    Identifier  "Westinghouse 37 LCD HDTV"
    HorizSync   30-48
    VertRefresh 50-75
      Modeline "1360x768"  84.72  1360 1424 1568 1776  768 769 772 795  -HSync +Vsync
EndSection
Section "Device"
    Identifier      "ASUS 9980U nVidia 5950"
    Driver          "nvidia"
    VideoRam        262144
    Option          "UseEvents" "True"
    Option          "RenderAccel" "true"
    Option          "XvmcUsesTextures"  "false"
EndSection
Section "Screen"
    Identifier  "Screen 1"
    Device      "ASUS nVidia 5950"
    Monitor     "Westinghouse 37 LCD HDTV"
    DefaultDepth 24
    Subsection "Display"
        Depth       8
        Modes       "1360x768" "1280x720" "1024x768" "640x480"
        ViewPort    0 0
    EndSubsection
    Subsection "Display"
        Depth       16
        Modes       "1360x768" "1280x720" "1024x768" "640x480"
        ViewPort    0 0
    EndSubsection
    Subsection "Display"
        Depth       24
        Modes       "1360x768" "1280x720" "1024x768" "640x480"
        ViewPort    0 0
    EndSubsection
EndSection
Section "ServerLayout"
    Identifier  "Simple Layout"
    Screen "Screen 1"
EndSection

[Shan]

Turns out, it had nothing to do with refresh rates, or Windows vs Linux settings or anything software at all. It was whats called "Ground Loop Interference". Basically, my cable line (which feeds into my Linux Box) had a different ground voltage (for lack of a better term) than that of my surge-protector. Whenever my MythTV box had the cable line attached, the two ground voltages caused interference, which my new TV was succeptable to. I didn't get the interference on my Laptop, because it was powered by battery and had no connection to the cable line.

Long story short, there are a few solutions to this problem, some simple, others not; so I'll leave those out (if you're really interested, use google on "Ground Loop Interference").

Simple solutions are either pickup a ground loop isolator / interrupt for around 50 bucks; the problem here being that most stores (Wal*Mart, Best Buy, Radioshack) carry them for audio systems, but not video systems, so if you need the piece in a hurry, you're likely out of luck (though some e-tailors sell them).

The other alternative is to pickup a surge-protector that includes cable / antenna grounding functionality such as the Monster Power AV700. What this does, is it re-grounds your cable / antenna coax line to the same grounding as the rest of your components, removing the loop interference.

Ah, Wikipedia, is there anything you can't tell us? http://en.wikipedia.org/wiki/Ground_loop_(electricity)

[sleepy boy]

This could be a coincidence, but I had the same problem,

Constant line shifting/stuttering around the bottom of the screen
(this only happened with 1366x768 resolution...)

This was on a Toshiba 32w300Ps

The problem did not seem to be ground loop interference, but it was a pc-input configuration option(on the TV) that I had to activate to make it stable

In the menu of my tv there was an option to enable the "WXGA input"

After enabling this the problem was solved