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I am using Windows 7 Ultimate with a Nvidia graphics card and two DVI monitors. I want to measure some signals on the second DVI output over the analog path (VSync, video signal) on an oscilloscope.

However when I disconnect the second monitor Windows automatically disables the DVI output. This is useful for home users but really annoying for me. Can I switch that feature off and how?

Update: It seems there is no solution for this. So I switched back to Windows XP for now.

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Are you sure it's Windows doing it? Try a Linux live-CD and see what happens? – Kevin Panko Aug 3 '10 at 15:51
XP doesn't do such things and I also don't think it's the graphics card driver. I had a look in the Nvidia control panel, but found nothing useful. See also here:… – asdrubael Aug 3 '10 at 18:59
Oh it's entirely possible to do this in Windows 7. You just have to open up your DVI cable, attach leads to the appropriate wires, and then measure. You're only going to destroy a totally good cable. – MBraedley Aug 12 '10 at 18:51

You could use a Video Terminator (Make one) then use the tap off the signal you need. This should work for you as Windows will still detect the Dummy Screen attached and keep the DVI on.

You may need a DVI- VGA.

Here is a link on how to turn your DVI-VGA into a terminator.

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