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I have a machine with a Quadro FX 580 card (DVI and two Displayport). Attached to it are two 19" Acer screens, which are both (annoyingly) VGA. The first one works perfectly, with a DVI->VGA adaptor.

The second one doesn't work. It's got a VGA cable, which goes into a VGA->DVI converted, which then goes into a DVI->Displayport converter. Initally, I was getting 'Cable Unplugged' on the screen, and it couldn't be seen by Windows or the nVidia control panel. After swapping the VGA->DVI adaptor (which works perfectly on another machine), Windows can now see the monitor. The nVidia panel sees the model and native resolution, but I get a constant 'No Signal' error. Switching to the other Displayport makes no difference.

I suspect that the card is seeing a DVI connection plugged into it (nVididaCP shows the monitor as having a DVI connection), and it only sending out a digital signal because of this. Does anyone know of a solution (other than trying to get a Displayport->VGA adaptor), or of a way to force the card to see it as VGA?

Thanks,

~Dentrasi

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up vote 1 down vote accepted

Edit: A DVI plug has a combination of digital and analog pins. There are different versions, sometimes pins are missing. A DVI -> VGA converter only channels the analog signal to the right pins, it doesn't (and can't) convert digital to analog. Your card has to provide both Digital and Analog: DVI-I.

A Displayport output is a digital output, it does not contain an analog signal. So the DP->DVI converter can only supply the digital-only DVI-D.

So, sadly, chaining DP -> DVI -> VGA cannot work.

It probably has only 1 A/D converter, that is kind of common for such cards. A D/A converter is relatively expensive. That would mean you can't get it to run 2 analog monitors.

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If DisplayPort only provides analogue, how can a device like this work? store.cbccomputers.com/products.asp?partno=DP2VGA –  Dentrasi Oct 9 '09 at 14:51
    
Looking at the picture it contains some electronics, so it probably has a D/A converter on board, powered by the DP. But my conclusion about DP->DVI->VGA stands. –  Henk Oct 9 '09 at 15:18

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