Cannot get 3rd monitor to work (radeon 7950)

[mp108]

Hello

I know this has already been asked, but I still find all the configurations hard to understand being a complete noob.

I have a radeon 7950, which has 2xmDP, 1 DVI and 1 HDMI outputs. I currently have 2 monitors attached like this:

DVI(monitor)->DVI(pc)
DVI(monitor)->DVI-to-miniDisplayPort converter (passive)

To connect the 3rd monitor I've tried these combinations but none of them work.

Config 1

DVI(monitor)->DVI(pc)
DVI(monitor)->DVI-to-miniDisplayPort converter (passive)
DVI(monitor)->DVI-to-miniDisplayPort converter (active)

(1) and (2) work only.

Config 2

DVI(monitor)->DVI(pc)
DVI(monitor)->DVI-to-miniDisplayPort converter (active)
DVI(monitor)->DVI-to-miniDisplayPort converter (active)

Only (1) works

Config 3

DVI(monitor)->DVI(pc)
DVI(monitor)->DVI-to-miniDisplayPort converter (active)

Only (1) works

Config 4

DVI(monitor)->DVI-to-miniDisplayPort converter (active)

Doesn't work at all (I tried both cables, and both ports, so can't be the cable/ports)


Anyone know what I'm doing wrong? It is just that 3 dvi's just won't work? (i.e. I have to use the hdmi - and if so do I need active or passive?)

Thanks in advance

 

[VincentP]

I guess from this that none of your monitors have a display port input. That would be the best solution.

If running 1920x1080 resolution at 60 Hz on each monitor, it wouldn't hurt to use the HDMI output of the card for one of your monitors. If the monitor does not have a HDMI input you can use a HDMI to DVI adapter or simply a HDMI to DVI cable.

At least one of the three monitors does have to be connected to the mini-display port output of the video card. I believe this needs to be an active adapter for use with a DVI monitor. It seems like none of your configurations above work with the active adapter you have. Are you sure that it is display port (output from graphics card) to DVI (monitor input) and not DVI to display port?

 

[mp108]

Thanks VincentP

I guess from this that none of your monitors have a display port input. That would be the best solution.

I have 2 Dells that have DVI, HDMI and DP - it's just that I've always used DVI for them, never thought to use DP. The 3rd monitor is an Asus which only has VGA and DVI.

So you reckon I should have (pc-to-mon): 1 DVI-DVI, 1 mDP-DP, 1mDP-DVI ? Do any of these have to be "active" cables?

Yes the graphics output is def mDP on the card end and DVI on the mon end.

Thanks

 

[VincentP]

Best would be to use a DVI to DVI cable for the Asus monitor, and mDP to DP cables for two Dell monitors, no adapters required.
mDP to DP adapters with DP to DP cables would be just as good for the Dell monitors.

The video signal of DP is different to DVI or HDMI. Avoid converting between them unless required.

"Yes the graphics output is def mDP on the card end and DVI on the mon end." - It's the adapter I am asking about. An active adapter will only work in one direction, i.e. DP to DVI is different to DVI to DP.

 

[mp108]

Best would be to use a DVI to DVI cable for the Asus monitor, and mDP to DP cables for two Dell monitors, no adapters required.
mDP to DP adapters with DP to DP cables would be just as good for the Dell monitors.

The video signal of DP is different to DVI or HDMI. Avoid converting between them unless required.

"Yes the graphics output is def mDP on the card end and DVI on the mon end." - It's the adapter I am asking about. An active adapter will only work in one direction, i.e. DP to DVI is different to DVI to DP.

Thanks I'll try as you say. The converters are indeed mDP to DVI.

 

[mp108]

Thanks VinceP works now.

This video was very helpful for complete novices like me: https://www.youtube.com/watch?v=Jf0X0lNFmgw

Nothing to do with active/passive cables. All i needed was 2 cheap mDP-to-DP cables. So the working setup is now:

1. DVI(mon)->DVI(pc)
2. DP(mon)->mDP(pc)
3. ditto