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I've got a client who has a graphics card with two DVI outputs.

He bought two brand new VGA screen yesterday, so I tried fitting them using two DVI to VGA adapters, one for each screen, but it doesn't work.

Someone told me you can't use two DVI to VGA adapters at the same time but Googling doesn't bring up any definitive answers. All the search results I get are about using one DVI screen and one VGA screen.

Is using two DVI to VGA adapters possible? If not, what might be the solution? How about a DVI adapter that splits into two VGAs?

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Whom ever told you, that your limited to a single adapter, didn't know what they were talking about. Have you tried a different brand of adapter? Have you verified each adapter works? How about the cables? –  Ramhound Nov 12 '13 at 16:08
    
I'm fairly certain one of the adapters doesn't work, but the cables are brand new. –  pappy Nov 12 '13 at 16:10
    
My experience has been that not all DVI ports support an adapter to VGA so it's probably not even related to merely having two adapters. –  MonkeyZeus Nov 12 '13 at 16:13
    
From Wikipedia - en.wikipedia.org/wiki/Digital_Visual_Interface - A passive DVI-to-VGA adapter. This adapter will NOT work with a DVI-D output. It requires a DVI-I or DVI-A output to get the analog signal to a VGA input (even if the adapter looks like a DVI-D). A more expensive active adapter (or converter) is required to connect DVI-D to VGA. –  MonkeyZeus Nov 12 '13 at 16:17
    
@ramhound My question was to find out if multiple DVI to VGA adapters work on a single graphics card. You don't need to know if I'm certain about my own adapters to be able to answer that. Please do keep your downvote if you think it is still necessary. –  pappy Nov 12 '13 at 16:20

2 Answers 2

up vote 2 down vote accepted

It largely depends on the make/model of the graphics card but the short answer is if its a modern card the likelihood is it won't be possible.

As you know, VGA is an analog standard. The DVI standard allows for outputs that support analog connections (DVI-A), digital connections (DVI-D) or both analog and digital integrated into one connector (DVI-I). The DVI to VGA adapter doesn't do anything clever, it just takes the analog pins from a DVI output and presents them in DSUB connector. If the output is DVI-D, these pins are missing (or unconnected) so it won't work.

If the graphics card is equipped with two DVI-I (analog-only is rare) connectors then you can connect two VGA adapters. However, most recently manufactured graphics cards are equipped with only one analog-enabled DVI port, the second is usually digital only.

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Do I want to buy two DVI-I adapters then? –  pappy Nov 12 '13 at 16:29
1  
@pappy - I thought you already had the adapters? You need to update your question to include if the graphic card uses DVI-D or DVI-I there is a huge difference. If your client's graphic card uses DVI-D then what you want is basically not possible, at least in the context of, spending as much money to convert the signal then it would take to actually purchase monitors that had DVI-D ports –  Ramhound Nov 12 '13 at 16:34
    
@djones good answer but the last point depends on the age of the graphics card. I haven't bought a graphics card in the past couple years, but I have several older cards with dual DVI-I outputs. –  rob Nov 12 '13 at 16:38
    
@pappy. Hi. You need to confirm with the manufacturer of the graphics if the card supports analog output on both DVI ports. –  user265618 Nov 12 '13 at 17:13

Typically, if the adapter can plug into the port, then it should work. a true DVI-D port will not have the pin holes for the VGA pins, and thus the adapter cannot be plugged in. Have you tried switching a single cable and adapter that works on one side to the other?

Check below to verify what type of connectors you are dealing with.

Ultimate DVI guide: http://www.ramelectronics.net/DVI_info.aspx

I'd stand by that one of the adapters or cables is bad. Switching a known working set could verify this. There is also the slight chance that the VGA port on them onitor is bad, but again swapping components can eliminate this. Finally, the card manufacturer was lazy and used DVI-I ports when not supported though I find that to be highly unlikely.

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He already confirmed one of the adapters was bad. –  Ramhound Nov 12 '13 at 16:33

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