R9 280x /HD 7970 in Mac Pro 4.1 without extra PSU?

Discussion in 'Mac Pro' started by ezroller, Feb 17, 2017.


Is the 280X/7970 doing OK in the 2009 Mac Pro?

  1. Yes. No problems, been running for quite some time now

  2. No, fried the board.

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  1. ezroller macrumors newbie


    Feb 16, 2017
    Been searching for something on what kind of experience people have from running a single 280x or 7970 in a Mac Pro 4.1 without an external PSU or using SATA power. Anyone who has actually fried/overheated/damaged their logic-board? Especially interested in those who have been running any of these cards in Final Cut Pro 10.3.x. While rendering I suspect the GPU goes full steam. I would also say that unless you have done the R17 mod, you won't be running it full speed, so…

    Let me know!

    For those who has been using SATA power, did you find a way to use power from other SATA-connectors than the optical bays?
  2. owbp macrumors 6502a


    Jan 28, 2016
    Belgrade, Serbia
    There is no need for anything but motherboard's PCIe connections to power those cards. You could make a splitter to equally divide load that card pulls from 6 and 8 pin slots but other than that it's all good.

    FCPX doesn't stress the GPU as much as some games or synthetic benchmarks do, so you're even safer if you'll use it just for that. :)

    I'm talking about "normal" Tahiti cards, not the ones from the last batch of production that are usually 3 slots tall and require two 8 pin connections. Never tried those or heard that anyone is using them in Mac Pro.

    Btw, I'm trying to downclock mine (MSI R9 280X) to use just one 6pin connection but cannot get the stable setting (quite possibly I never will).
  3. Supermacguy macrumors 6502

    Jan 3, 2008
    I have a 7970 in my 4,1 and been using it for more than a year without problems. No extra power supply. I only use FCP occasionally.
  4. ezroller thread starter macrumors newbie


    Feb 16, 2017
    The cards I'm planning on using for mine and my colleagues machines are Sapphire R9 280X Dual-X (basically a advanced cooling-setup) and Ref-spec 7970. From what I have seen, both seem to run at 867Mhz and both use one each of 6/8-pin connectors. I have a XFX 7970 GHz in my RatMac hack, and it indicates full load on the GPU when rendering from FCPX or Compressor, but the fans never seem to run faster than 50%. So I guess OpenCL isn't that hard on power, maybe doesn't stress GPU-RAM as much as gaming or Luxmark. Solid performer as it does the BruceX 5K (cache cleaned) in 21s on 10.11.6, and my machine only has a i3 3225. So your responses are pleasant to read. :)
  5. h9826790, Feb 17, 2017
    Last edited: Feb 19, 2017

    h9826790 macrumors G3


    Apr 3, 2014
    Hong Kong
    FCPX is not that demanding on power consumption.


    R17 mod won't make any difference when the card is installed in a X16 slot.

    Running a single 7970 / R9 280X without extra is easy. A simple mini 6-> 8 pin cable can do the job. However, depends on the card's firmware, the 8 pin on some card can draw too much (>120W) which may shutdown the cMP (safe protection) under high stress. Therefore, just a bridge to balance the loading between 2x mini 6pin as owbp state is the way to go. Of course, you may consider to utilise the SATA power as well, but that's unnecessary (except you want the power draw stay below the official max 75W for each mini 6pin under real 100% stress e.g. Furmark).
  6. Ph.D., Feb 18, 2017
    Last edited: Feb 18, 2017

    Ph.D. macrumors 6502

    Jul 8, 2014
    I have a 280X (MSI 3 GB with a modest factory "overclock" and a pretty decent cooler) in a 3,1. I used the supplied 8-pin to 6-pin adapter for normal dual 6-pin power provision. I did the R17 mod, though I don't think that makes a material difference.

    This has run perfectly for a few years now, with the exception of a single game, which occasionally results in system shutdowns (not often enough to cause more than surprise, i.e. very occasionally). The card is capable, at least in principle, of drawing slightly too much power under extreme loads. Thankfully, nothing has ever been damaged, and such shutdowns are likely the system's protection acting correctly. I've never had much worry about it.

    So, from my experience I'd say it's O.K., if slightly on the margins.
  7. owbp macrumors 6502a


    Jan 28, 2016
    Belgrade, Serbia
    @Ph.D. I think that the main problem, in your case, is the 8 pin PCIe. The cards BIOS is telling the card to pull most of its power from it since it is rated at 150W. So, you could have the situation as I had with Gigabyte HD7950 and it can be easily fixed.
    At the moment I have the same card, MSI R9 280X Gaming 3G, and all is good. Even in most demanding Windows games.
    But I have that X cable that goes from motherboard and then devides the power to 8 and 6 pins to the card.
    So, now card sees 17Amps delivered to it (3A from 16x PCIe MB Connection, 4A from 6 pin and 10A from 8 pin) but Mac only sees 3A from 16x PCIe and 7A maximum from each 6pin slot.
    The easiest way, if you don't want to soldier pins on your GPU is to get 2x6pin to 8pin (from mobo) and then go from that 8pin to 6 and 8 pin to your card.
  8. Ph.D. macrumors 6502

    Jul 8, 2014
    So you are saying to merge the two 6-pin motherboard sources so that one isn't potentially bearing more of the load - I like the idea.

    Anyway, thanks, but I don't play that game on it anymore, nor do I do anything that stresses the card much these days, so I don't think it's much of a concern for me now. I've moved to a Skylake linux system with GTX-1070 for performance-related tasks.
  9. Zwhaler macrumors 603


    Jun 10, 2006
    As others have stated, due to the 150W concern out of the 8pin, I personally connected the two pins to an external GPU power supply that I purchased separately, and very inexpensively I might add. The card is plugged in to the PCIe slot in the Mac Pro, but each of the pins are connected to the external PSU (which is connected to SATA from the 2nd super drive so it turns on with the Mac Pro).

    I haven't had any problems related to power draw, which was the point. Whether or not I would have encountered issues had I plugged in directly, I do not know. I use it mostly for FCP X and can do some serious rendering, which is why I opted for external PSU since I did not want any problems, given that I anticipate running it at full load for much of the time. If you have any more questions, feel free to ask.

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