I recently purchased both a Dell P2715Q 27" 4K monitor and a 13" 2015 rMBP. The monitor is not recognized when I plug the laptop into the monitor via the monitor's provided DP cable (into either Thunderbolt port). When I plug in the laptop using the Monitor's HDMI cable, it shows up and can render at 4K, but only at 30Hz. I also tried plugging the laptop into another display with HDMI and that one also worked fine. Unfortunately, I don't have access to another display that has a DP port. My research prior to purchasing the laptop and monitor suggested that I should be able to connect them easy-peasy and get 4K at 60hz using either MST or SST signalling. However, I am very new to Macs, so my question is whether or not I need to do something special to get this to work? A Thunderbolt to DP cable perhaps? The monitor also has a miniDP port as well, do I have to use that? Did I somehow end up with a broken DP cable?

Any ideas?

  • is there a menu option on the display to force it into SST mode?
    – Alnitak
    Apr 10 '15 at 20:10
  • According to the manual for the display, it works in SST by default. And I can't find any settings in the OSD for the monitor to switch it to MST (in fact, the option is disabled).
    – syazdani
    Apr 11 '15 at 0:27
  • These are the instructions for changing the monitor to MST mode: dell.com/support/article/us/en/19/SLN296015/EN
    – syazdani
    Apr 11 '15 at 0:55
  • I hope you find an answer - I've got my rMBP 2015 on its way and I was planning to buy this same monitor to go with it!
    – Alnitak
    Apr 11 '15 at 7:16
  • 1
    Apparently 10.10.3 has improved support for 3840x2160 @ 60 Hz SST.
    – Alnitak
    Apr 13 '15 at 15:39

So oddly enough, 10.10.3 didn't seem to make any difference, but the supplemental update that came up yesterday (14D130a) on Software Update (http://9to5mac.com/2015/04/16/apple-releases-os-x-10-10-3-supplemental-update-to-fix-startup-issue/) fixed it right up. Now when I connect the display via Thunderbolt, it comes up at the native 4K resolution at 60hz running in SST mode. Thanks everybody for your help!

  • I'm pleased to say I just received my P2715Q and it worked out of the box on 10.10.3 with all updates applied :)
    – Alnitak
    Jun 17 '15 at 12:35
  • Thank you for your update. Could you please help sharing what are scale resolutions available on your 4k monitor? Thank you in advance! Jul 30 '15 at 0:23
  • @RatanachaiS. I'm not sure what you are asking for. I can definitely get the info for you if you point me in the right direction though :)
    – syazdani
    Jul 31 '15 at 13:57
  • 1
    @RatanachaiS.: the options are 1280x720, 1920x1080, 2560x1440, 3008x1692, 3840x2160. But please be aware of the OS X resolution scaling issue: forums.macrumors.com/threads/…. tl;dr, the non native and non-pixel doubled resolutions can be pretty laggy because of the way that OS X does retina resolutions.
    – syazdani
    Aug 7 '15 at 3:08
  • 1
    You are all lucky if it's working well for you. I have had a miserable experience. I have a 13-inch, early 2015 MB Pro Retina with a 3.1 GHz i7 & 16 GB of RAM, running Yosemite and now El Capitan. This monitor does NOT work with a thunderbolt/mini-dp cable at all. It has only ever worked with the supplied mini-dp to display port cable, but it capriciously often doesn't work. Thinking that it a cable issue, I got another one. However, it still frequently chooses not work. It's not a MacBook port issue, because it works fine with a Thunderbolt display, implying a Dell engineering problem.
    – Subfuzion
    Oct 7 '15 at 20:21

From Everymac

*This model supports a simultaneous maximum resolution up to 3840x2160 on two external displays via Thunderbolt 2. Alternately, it can support a single display up to 3840x2160 via Thunderbolt 2 and a single 1080p display at up to 60 Hz, 3840x2160 at 30 Hz, or 4096x2160 at 24 Hz via HDMI.

afaik, Macs don't do MST


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .