Radeon 7950 Mac Edition wont display 3 monitors on MacPro 3,1

Discussion in 'Mac Pro' started by digitaltrader, Mar 24, 2014.

  1. digitaltrader macrumors newbie

    Aug 22, 2006
    I recently purchased a Saphire 7950 Mac edition to replace the stock video card in a Mac Pro 3,1 running 10.9.2. I am running 3 DVI monitors (2 at 1200x1600 resolution and the 3rd at 2560x1600). I bought 2 active mini displayport adapters and use the DVI connection for the higher resolution monitor. I can successfully setup 2 monitors as long as I use a passive mini displayport to DVI adapter . As soon as I plug in an active mini displayport to DVI adapter the computer reboots. Because of this I can only use 2 monitors as the passive adapters will only allow one monitor connection. I have even tried a Saphire branded active adapter that still causes the computer reboot immediately when plugged in. Any suggestions?
  2. ashman70, Mar 24, 2014
    Last edited: Mar 24, 2014

    ashman70 macrumors 6502a

    Dec 20, 2010
    What slot do you have the card in?


    Found this in an amazon review, seems you need an adapter for the PCIe connector to drive more then 2 monitors. Also it appears others have had issues with this card on Mac Pro 3,1 models since they have only 2 PCIe 2.0 slots, people using Mac Pro 4,1 and 5,1 models don't seem to have issues. I don't think enough power is getting to the card unless you get the 6 pin PCIe power splitter and that may be causing it to reboot when you try the third monitor.

    "Great card, works for my purpose but has a few things you should be aware of...

    First, it takes TWO PCIe power cables, meaning if you are like me and have more than a couple monitors (I have 4) then you will have to get a 6 pin PCIe power splitter to make more than one card work.

    Second, since I did not yet have the splitter I tried this on 4 monitors, then three then just two of my Mac 27" 2012 monitors and it pixilated like crazy, it could not handle the resolution of two high end monitors, let alone 4. It WILL drive 4 but if you do anything graphical forget about it, if you are just surfing it might be fine."
  3. digitaltrader thread starter macrumors newbie

    Aug 22, 2006
    Its in slot one (16x)
  4. ashman70 macrumors 6502a

    Dec 20, 2010
    Try the six pin power splitter, it should fix the problem.
  5. digitaltrader thread starter macrumors newbie

    Aug 22, 2006
    I have the 2 six pin power plugs already connected. Is this what you are referring to?
  6. ashman70 macrumors 6502a

    Dec 20, 2010
    I guess it seems the guy in the Amazon review had more then one video card and one PCIe power cable was powering his other card, so he needed an adapter so that he had both power connectors in the 7950. Not sure then what is causing your system to reboot. I assume you are running the latest version of Mavericks? Maybe try moving the card to slot 2, but not sure why that would work over slot 1, give it a try, stranger things have happened.
  7. matelg macrumors newbie

    Dec 2, 2016
    did you solve this issue? I have the same issue with Sappharie HD 7950 Mac Flashed

  8. ActionableMango macrumors G3


    Sep 21, 2010
    Very high chance the problem is that you are using three legacy connections. Describe the ports you are using on the card, the cables and any adapters you are using, and which ports on the monitors are being used.
  9. Softsand macrumors newbie

    Dec 1, 2016
    I tried all sorts of things - different connectors, active adapters and nothing worked on a flashed Powercolor HD7950.

    Bought a Gigabyte RX460 and with one monitor connected directly via DP, I now have 3 monitors !

    Quieter, cooler and less power consumption too.
  10. ActionableMango macrumors G3


    Sep 21, 2010
    Oh right, it's a flashed card. I don't know much about flashed AMD cards, but non working ports seems to be a common problem. Inappropriate ROM or something like that.
  11. Fl0r!an macrumors 6502a

    Aug 14, 2007
    Flashed AMD cards can drive 3 or 4 displays when respecting the "no more than 2 legacy connections" rule. Of course the experience may vary when the card has been badly flashed or had an incompatible port layout in the first place.
  12. matelg macrumors newbie

    Dec 2, 2016
    The card have:
    1 DVI
    1 HDMI
    2 Mini DP

    In terms of cables

    I tried with DVI + HDMI + 1 Mini DP

    The mini DP is an adaptor to HDMI

    So do I have to understand the DVI is legacy connection, therefore if I buy another mDP to HDMI adaptor should work (1 via HDMI + 2 MiniDP with adaptor to HDMI)?

    --- Post Merged, Dec 5, 2016 ---
    Is there any in particular (flashing method) that you can advice?

    Thank you in advance
  13. Fl0r!an macrumors 6502a

    Aug 14, 2007
    The only "correct" way involves taking the original PC VBIOS and attaching the Mac EFI to it, as described in the "7xxx testing thread" @ netkas.org.
  14. ActionableMango macrumors G3


    Sep 21, 2010
    I think there are two likely scenarios:

    (1) It is normal for this card to only support two legacy connections (anything prior to DisplayPort), so if you have three legacy connections, one of them won't work. DVI and HDMI are legacy, so that's two right there.

    The MiniDP to HDMI adapter will count as a legacy connection (HDMI) unless the adapter is specifically an "active" adapter, which costs a little bit more. So that's three legacy connections unless you are certain it is an "active" adapter. If this scenario is the case, the fix is to buy a proper "active" adapter.

    (2) You have an improper flash and so one of the ports isn't working.
  15. UKenGB macrumors member

    Feb 21, 2010
    Surrey, UK
    Old thread, but I recently experienced this problem with 3 Apple Cinema Displays (1x30” + 2x20”) connected to an HD7950 in a Mac Pro 5,1. With regular mDP -> DVI adapters for the 20” displays, only one would work (first one to be plugged in) simultaneously with the 30”.

    Having ascertained I needed ACTIVE adapters, but not prepared to pay an exorbitant £125 each for 2 of Apple’s gizmos, I chanced my luck with a pair of these:-

    YouN Active Mini Displayport DP to DVI Cord Cable Adapter Eyefinity Supported HD

    At merely £5 each, I thought it probably too good to be true, but once the 2 20” displays were connected via these adapters, I had all 3 displays running perfectly. Yay!

    Hope this might help others with the same issue.

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