No Video

[LunarMist]

I have a monitor with 2 digital inputs that has been in use for a couple of years. One digital to digital cable connects to the main computer and works fine. I have been using a digital to VGA cable on the other input to connect to the older, backup computer. Switching via the monitor front panel switch works fine.

Lately I have become annoyed with the analog quality of the video from the old computer and decided to put in a "newer" AGP card (matrox P650). The strange part is that there is no signal when the digital to digital cable is used, but the analog signal is fine if I put the other cable in its place. Obviously there is nothing wrong with the digital cable since it works perfectly with the main computer. Am I doing something wrong?
Thanks.

 

[blakerwry]

Did you try booting with the digital/digital cable in place... Most cards seem to initialize outputs on bootup and will set the default output based on their initialization order and what they see connected first. If nothing is connected on bootup they will likely initialize VGA over DVI or S-Video(in my experience).

You'll also want to check your OS/Driver settings as some drivers seem to have a preferred output method. In these instances, a few clicks in the video properties usually sets things straight.

 

[LunarMist]

Did you try booting with the digital/digital cable in place... Most cards seem to initialize outputs on bootup and will set the default output based on their initialization order and what they see connected first. If nothing is connected on bootup they will likely initialize VGA over DVI or S-Video(in my experience).

Thanks, that seems to be the cause. Unfortunately when the 2nd computer boots the primary computer is already running and the display's input automatically switches back to it if nothing is found on the other input after about 2 seconds. It may be possible for the 2nd computer to find the card if I poke the LCD display's input button at the right time during boot, but hardly an ideal solution (I don't have a second DVI/DVI cable at the moment to test with).

 

[blakerwry]

I imagine getting the second cable will fix the issue for you. However, I have heard of some people modifying the video card BIOS to set the preferred output method... not really a thing for the faint of heart.

Then there is the OS, which under the right circumstances can be told to override all video card settings. The trick is whether the drivers allow this or if you need a 3rd party app like PowerStrip to get the job done.

 

[P5-133XL]

You can also deal with the issue using a Digital KVM: Only hooking up the video/monitor and directly hooking up the KB and Mouse to your computer. Unfortunately this will require at least one more cable and, of course the KVM: So try just getting a second cable first

 

[ddrueding]

Then there is the OS, which under the right circumstances can be told to override all video card settings. The trick is whether the drivers allow this or if you need a 3rd party app like PowerStrip to get the job done.

This is significant. I know with my system the BIOS occasionally chooses to prioritize one of the other monitors I have connected (that are typically off). When this happens, the screen is in standby during the entire boot process, until Windows loads and finally takes control of the display adapters. If you haven't given the system enough time to boot all the way to desktop, you might want to try.

Edit: Video cards are a 7950GT and a 7900GS.

 

[LunarMist]

Update: The setup works fine with the two DVI cables if the main system is on LCD input 2 and the second computer is on input 1. (Don't ask why.) Oddly, the new DVI cable has about half of the pins missing yet image quality is fine. Am I missing something?

 

[blakerwry]

The new cable is probably a single link, the old a dual link.

 

[LunarMist]

What is the difference, or is it only needed with the newer LCDs and faster video cards? I don't see anything.

 

[ddrueding]

Dual Link supports higher resolution (>1920x1080, IIRC)

 

[timwhit]

Dual Link supports higher resolution (>1920x1080, IIRC)

Correct:

(Single) WUXGA 1920 × 1200 @ 60 Hz
(Dual) WQXGA (2560 × 1600) @ 60 Hz

 

[LunarMist]

Thanks. My monitor has no resolution, so there is no problem.

 

[Jan Kivar]

Did you try booting with the digital/digital cable in place... Most cards seem to initialize outputs on bootup and will set the default output based on their initialization order and what they see connected first. If nothing is connected on bootup they will likely initialize VGA over DVI or S-Video(in my experience).

Thanks, that seems to be the cause. Unfortunately when the 2nd computer boots the primary computer is already running and the display's input automatically switches back to it if nothing is found on the other input after about 2 seconds. It may be possible for the 2nd computer to find the card if I poke the LCD display's input button at the right time during boot, but hardly an ideal solution (I don't have a second DVI/DVI cable at the moment to test with).

Have you tried to disable the automatic input detection from the monitor?

Cheers,

Jan

 

[LunarMist]

I don't know, but it is OK the way I described. It would be better with a KVM switch, but that would require more cables. I don't think there any KVM switches for DVI + PS/2.