Issue with 3rd Monitor Mac Pro

[Jigga Beef]

Hello All

I have 3 X 28 Inch Samsung monitors. They are all working fine.

I just installed a 2nd video card in my Mac Pro 5,1 so I could run a third display.

First card: ATI Radeon HD 5770 1 GB
1) has 2 DVI Inputs, 1 HDMI input and 1 Display port Input

Second Card (newer)
2) 2 X Mini Displayports
1) DVI Port


I have had all my monitors hooked up and working but I wanted to run them all off Display ports.

I can't seem to get the all 3 monitors to work at the same time with just display port connections though.

Monitor 1 works fine Display port to display port

But when I hook up the 2nd and third monitor with display port to mini DisplayPort cords only 1 will show. The card doesn't seem to be able to show both monitors at the same time. When i check displays in System Pref. It shows 3 monitors but does one display is always black.


Any ideas?

 

[MarkC426]

You don't specify what the second (newer) card is!
What resolution are you running, do you really need dp connections?

 

[usna92]

Many video cards with both display ports and DVI will only display on one or the other. Meaning one of the Display ports and the DVI port are linked to the same video output channel. That is why on a card with two DVI output and a display port, one of the DVI will be a different color. You will need to make sure that you have sufficient video output channels for all the connectors that you want to use. As the other poster said, it will depend on what the second video card is. Additionally, the depending on the power of the card, the size of the monitors connected to it may limit whether it can support one or two monitors at your desired output resolution.

Steps
1. Make sure that at least one of the cards you are using can power two 28" monitors at your desired resolution.
2. Make sure you are not connected to a set of paired connectors on the video card with two monitors.

 

[Jigga Beef]

So the issue isn't specific to 1 video card right now I am running 1 monitor HDMI on my 1st video card

And 2 displays on the 2nd video card though Mini Display port.

Just can't seem to have 3 display ports hooked up at once even between 2 cards.
[doublepost=1508869712][/doublepost]

You don't specify what the second (newer) card is!
What resolution are you running, do you really need dp connections?

It's the exact same card just different output's on the back.

I don't "need" them but I have the cords and they slots.

Right now they are all on 1080 but i figured using all the same connections would be better.

Just odd that the other card can't power just 1 monitor vis display port but it can via HDMI

 

[MarkC426]

If they are the 'exact same cards' they will have the exact same outputs?

I used to have two identical 5770's, with two 24 inch monitors (one on each) and an oculus rift using hdmi on one without issue. Before I had the second card I had the two monitors on the one card (one dvi, one mini dp).

If you are only displaying at 1080, there is no benefit using dp, just use dvi/hdmi.

 

[Jigga Beef]

If they are the 'exact same cards' they will have the exact same outputs?

I used to have two identical 5770's, with two 24 inch monitors (one on each) and an oculus rift using hdmi on one without issue. Before I had the second card I had the two monitors on the one card (one dvi, one mini dp).

If you are only displaying at 1080, there is no benefit using dp, just use dvi/hdmi.

Per System Preferences it says

ATI Radeon HD 5770 Slot 1
ATI Radeon HD 5770 Slot 2

 

[MarkC426]

If you want two connected to one card, just use dvi and mdp.
Unless you are at higher resolutions there is no need to have both on dp.

Your first card is not a mac efi card btw, it should have 1 dvi and 2 mdp.
Is this a flashed or pc card (this might be the problem).

 

[HighMacGuy]

You need active mdp to HDMI connectors. I used these:
https://smile.amazon.com/gp/product/B00PJ3LSIG/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

 

[h9826790]

If you want two connected to one card, just use dvi and mdp.
Unless you are at higher resolutions there is no need to have both on dp.

Your first card is not a mac efi card btw, it should have 1 dvi and 2 mdp.
Is this a flashed or pc card (this might be the problem).

If ANY of his 5770 is a flashed card or Apple card, the non reference one may be in trouble. Even though the Apple EFI is on another card, but the Mac will automatically apply the EFI info onto the other 5770 as well. Which highly likely will cause it to run with the wrong frame buffer. (I tested this on my HD7950 and R9 280 dual card setup. As long as one of the card boot from the Mac EFI ROM, the other card will able to show boot screen as well.

However, since he said the 2nd card is a newer card, I bet none of his 5770 are the Apple stock GPU, and may be both are PC GPU.

 

[Hugus Maximus]

Does anybody have any idea why simply using a Sapphire 5770 GDDR5 doesn't display 3 separate monitors? I have 2 DVI connected and the 3rd is the DP output > HDMI (connected with simple cable adapter) .... all three produce a picture but the DP output is now the first to boot and it is mirrored in one of the DVI outputs .... how do I get 3 independent monitors? Any help - much appreciated.

I have another thread running here with more information:
https://forums.macrumors.com/threads/3rd-monitor-issue-with-sapphire-7550gddr5.2146579/

But sadly no responses. (aside from an update I posted)

:-(