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I just bought Sapphire HD 7990 and I want to put 3 monitors on it.

This card has 5 outputs.

1x DVI-D and 4x Mini DisplayPort.

I connected my 2 other monitors and they work great, but my third monitor doesn't.

It is a 5-year old Asus TFT 19" 1440x900 monitor which ONLY connects via VGA. The graphics card gave me a bunch of adapters along and I chose the one that was miniDP to DVI-I (*edit: and then another adapter DVI-I to VGA) but it doesnt exactly work. My PC recognises the monitor, its model number and maximum resolution but the monitor claims it receives no signal. The monitor works perfectly fine when connecting to other devices via VGA.

What cable/adapter should I buy or is there anything else I can do?

Thanks in advance.

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migrated from electronics.stackexchange.com Sep 7 '13 at 22:22

This question came from our site for electronics and electrical engineering professionals, students, and enthusiasts.

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Are you sure your Operating System supports more than 2 monitors? BTW I think the question is off topic for this stack. –  jippie Sep 7 '13 at 21:11
    
My recommendation is to simplify. With MiniDP -> DVI -> VGA you may be losing signal. Try to connect the monitor to the DVI port using the adapter. I've been checking and it seems DVI-I and DVI-D are cross-compatible. –  Doktoro Reichard Sep 7 '13 at 22:26
    
How are the other 2 monitors connected? Are they VGA as well? Or are you using direct Mini DisplayPort on them? I know this sounds stupid, but have you tried rebooting? One of the weird quirks I've found with Windows is when connecting new monitors, even though it recognizes it, you sometimes have to reboot before it works correctly. –  druciferre Sep 7 '13 at 22:32

1 Answer 1

Mini DisplayPort is digital only.

DVI-I supports both ancient analog signal and modern digital signals. Converting the DP signal to DVI-D is easy, but it will only supply the digital signal on the DVI-I plug.

DVI to VGA can be easy if you convert the analog signal from a DVI-I or DVI-A connector to the VGA connector.

However in your case this signal is NOT present. You will need more than just a simple plug to 'convert' things. You will need an actual active component.

enter image description here

What cable/adapter should I buy or is there anything else I can do?

No pure cable will work in your case.

You either need an active convertor which converts digital information to an analog format (which start around 30 euro and upwards) or you need to change to aa monitor which understands a modern format. (VGA is truly ancient. It only stayed around because unlike DVI and HDMI it had no extra license costs to equipt a monitor with VGA/DB15).

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