[kwlug-disc] Confession (DVI)

Chris Irwin chris at chrisirwin.ca
Mon Mar 8 15:52:12 EST 2010

On Mon, Mar 8, 2010 at 14:07, Richard Weait <richard at weait.com> wrote:
> What I'm getting:
> - unplug working video card -> vga cable -> vga monitor input
> - connect same video card -> DVI-D cable -> DVI input on same monitor
> - Monitor says, "check video cable" in an accusing manner.

As Adam mentioned, (most?) video cards disable outputs that are not
being used. A DVI-I port (what's on your video card) actually carries
two different video signals: DVI-A (Analog, essentially your VGA
output) and DVI-D (Digital, this is what you're after). When the card
detects only -A in use (your DVI->VGA dongle) it disables the digital

If I recall, depending on certain factors like power supply and
motherboard, these settings can even persist unless you actually kill
power to the box by either yanking the cord or flipping the power
supply off.

I know my server goes as far as disabling the DVI-D output if there is
no monitor connected at boot. I have it hooked up to the same DVI KVM
as my desktop and laptop. If I don't switch to my server output when I
bounce the machine I will never get *anything* to the screen.

> Sure, I've tried.  I don't want to be the Luddite on my block.  I've tried:
> - multiple monitors with DVI inputs (HP, two different model numbers)
> - multiple video cards with DVI outputs (radeons and an nvidia)

This is odd. Are you actually swapping out video cards and it is still
not working?? I don't know what to tell you then.

> rage-filled seething cauldron of hate that is my approach to trouble
> shooting.

That's the best kind of troubleshooting. My significant other
suggested I build an angry dome when I was troubleshooting a flakey
wireless card.


> Must these video cards be tweaked
> by a DVI-D driver to output for a DVI-D cable?  Is there a particular
> sacrifice required?  Do these cards usually need to change jumper
> settings for DVI-D?

No, it should just work. I've never had to tweak my drivers for
primary output, whether it be VGA or DVI. (Not talking about hot-plug
laptop outputs, here).

Chris Irwin
<chris at chrisirwin.ca>

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