Thunderbolt 3 Dock - Displayport - Dell 4k Issue

Discussion in 'Mac Accessories' started by Wuzakee, Jul 18, 2017.

  1. Wuzakee macrumors newbie


    Jun 15, 2017
    I've had issues with two different thunderbolt 3 docks connecting to a 27" Dell 4k monitor using a DisplayPort cable. The laptop recognizes it's hooked up to the monitor and displays it correctly at 60 hz in system report, but the monitor continuously flickers (portions of the screen quickly shift) and turns on and off (every few seconds at best, sometimes several times per second).

    2017 MacBook Pro 15"
    Belkin Thunderbolt 3 Dock
    Kensington Thunderbolt 3 Dock (bought it when I thought maybe the Belkin was at fault).
    Dell 2715Q 27" 4K Monitor

    I've tried with three different display port to display port cables. The third one, I ordered specifically to make sure it was VESA certified 1.2.

    There is no problem using any of the DisplayPort cables from my PC or a Mini DisplayPort to display port cable with my earlier MacBook Pro. I can also use a USB-C to DisplayPort cable with no problem, both directly from the 2017 MacBook Pro or through either of the Thunderbolt 3 docks. I've also tried swapping around the Belkin and Kensington supplied Thunderbolt 3 cables.

    Everything else with the docks works.

    Unfortunately, I'm out of different cables/adaptors, and certainly no more 4k monitors to try out. Although it works, I don't want to tie up one of the dock's limited Thunderbolt 3 ports to go the USB-C to DisplayPort route.

    Has any one had any similar issues? Appreciate any help.
  2. dechols macrumors newbie


    Jul 23, 2017
    I had the same thing happen.

    I have the Dell 27" 4K display, recently got a 2017 15" MacBook Pro and the Elgato Thunderbolt 3 dock. When I connected the dock to the display via DisplayPort, it would either flicker or disconnect briefly every 15 seconds or so.

    I just returned the Elgato dock, but now I'm seeing that the problem wasn't specific to this dock.

  3. iregret macrumors 6502a

    Jan 23, 2012
    Posts like these make me wonder if perhaps an eGPU setup would be a better solution? I have 2 P2415Q Dell monitors I'd like to connect to a 2017 15" MacBook Pro. (It hasn't arrived yet.) I'm currently using a 2013 15" MacBook Pro and it's working wonderfully.

    At $300 for a dock that would theoretically support my 2 4K monitors, I wonder if spending a bit more on an eGPU setup would be better? All I really care about is the monitors and I've read that there are eGPU docks that charge the MacBook as well.

  4. dechols macrumors newbie


    Jul 23, 2017
    For your setup, I'd go with an egpu that can supply power to your MacBook. You won't get the extra ports (USB A, Ethernet), but the egpu obviously has other advantages.

  5. Wuzakee thread starter macrumors newbie


    Jun 15, 2017
    Anyone else with this monitor (2715Q) - can you confirm if your T3 dock using the DisplayPort cable works? For the record, the in-monitor MST option (off by default) remains off.

    Kensington tech support suggested a PRAM and SMC reset.
    Dell was useless, nonsensical script.
    On hold with Belkin...

    No longer have the Belkin (return period up), have a little more time with the Kensington.
    --- Post Merged, Jul 25, 2017 ---
    Belkin just said it sounded like it was defective. Here's a link to discussion about the same DisplayPort issue, using a Caldigit dock.!topic/macenterprise/9HQJrpuz0KA

    Just seems odd, I haven't heard any problems with any of these docks either than with the DisplayPort.
  6. dyn macrumors 68030

    Aug 8, 2009
  7. peeeeter macrumors newbie

    Aug 7, 2017
    I have the same problem on a Dell P2415Q with a CalDigit Lite. 30Hz/60Hz refresh rates, and even when forced to lower resolution. Works fine when connected directly via a TB3->DP cable (I get full 4k/60Hz, perfect performance). It seems like there is some defective chip/chipset that all these manufacturers use.
  8. Wuzakee thread starter macrumors newbie


    Jun 15, 2017
    Thanks for posting the suggestions from Caldigit - good that they acknowledge something's up. I did order a short (less than 1 m) cable specifically for this, and it also does not work.

    Quick summary, now that I've tried two different MacBook Pro's, 2 Dell monitors (a 27" 4k and a 32" 4k), many cables, a Kensington dock and two Belkins. I could never get a DisplayPort cable to work. A DisplayPort to mini-displayport cable "sort -of" worked. It connected, and everything looked great, but over the course of even 30 minutes it went down hill from flickering once every few minutes to every few seconds, and powering on and off the monitor. That happened from two different 2017 MacBook pro's.

    In the end, only solution is to use up the only free thunderbolt-3 port with a usb-c to DisplayPort cable.

    If I ever get enough motivation, I'd write to each of the dock manufacturers and hope someone gives a reply. There's no way that the techs that actually make the docks don't know exactly why this happens.
  9. KvB@Cologne, Oct 28, 2017
    Last edited: Oct 28, 2017

    KvB@Cologne macrumors newbie


    Oct 28, 2017
    Greetings from Germany Folks!

    I am encountering the same problem. Config:
    - 2017 MBPro 13" with touch bar / 8GB RAM / running High Sierra 10.12.6
    - Dell P2715Q bought late 2015
    - Belkin Thunderbolt 3 Dock bought Sept 17

    The Thunderbolt 3 dock is connected to the MBPro via the short USB-C / Thunderbolt 3 cable that came with the dock. Monitor connected to Belkin Dock via short (1meter) regular size dp to dp cable made by CROMO. Bought the cable because I got an advise from another blog that this might solve the problem.

    As long as I run the monitor in 30Hz mode (MST set to secondary) all works fine. If I switch MST off, hence running the monitor at 60Hz with 3840x2160 resolution flickering would start. Initially maybe once every 5sec, intensifying to once every 2sec as time goes on.

    I suspect all would work well if I connect the monitor directly to the other Thunderbolt 3 port on the MB Pro. But I bought the Belkin dock to avoid exactly that. I wanted to have a clean setup with only one cable running between the Belkin dock and the MBPro.

    I would agree that the Belkin technicians must have come across this issue when engineering the unit. Hence they should have an answer.

    Best Regards
  10. Fishrrman macrumors G4


    Feb 20, 2009

    Have you tried a -direct connection- from the MacBook to the display?
    If so, does it work?

    If it -does- work, the best advice I can give is, "forget the dock and go with what works for you".
    Not much more that can be said.

    Seems like thunderbolt "docking technology" isn't really all that it's cracked up to least not yet. (sigh)

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