15" tMBP: External USB-C display not working properly after sleep with High Sierra

Discussion in 'macOS High Sierra (10.13)' started by ManuCH, Sep 28, 2017.

  1. ManuCH, Sep 28, 2017
    Last edited: Sep 28, 2017

    ManuCH macrumors 6502a

    May 7, 2009
    Since upgrading to macOS High Sierra 10.13, I've been having an issue with my late 2016 15" MacBook Pro (Radeon Pro 455 graphic card). The problem is still there on High Sierra 10.13.1 Beta 1.

    I'm using it connected to an Asus MX27UC 4K USB-C display. After waking up the MBP from sleep, the external screen picture will not stay on. It will lose sync every 10 seconds or so, only to work again a couple of seconds later. It will basically flash on-off in a 10-2 second rhythm.

    Subsequent sleeps and resumes, as well as unplugging and re-plugging the display to USB-C will not help. A reboot also won't help. The only fix is to shut down the MBP and start it up again. Then it will work - until the next sleep.

    This can also be reproduced by unplugging and re-plugging the display to USB-C while the Mac is running. It seems that it will only sync properly on the first time after booting. On subsequent syncs it will fail. Disabling "automatic graphics switching" to leave the Radeon 455 always on doesn't help either.

    It only happens when using the display in its native DisplayPort over USB-C mode. If I connect it through a USB-C to HDMI adapter it works properly.

    It seems like they screwed up the Radeon display drivers with High Sierra.

    Is anyone experiencing similar issues with external displays?
  2. ManuCH thread starter macrumors 6502a

    May 7, 2009
    I have tried several ways of connecting the display. Results:
    - USB-C native connection: does not work
    - USB-C to DisplayPort cable: does not work
    - DisplayPort output from an Elgato Thunderbolt 3 Dock: does not work
    - USB-C to HDMI adapter: works

    So it seems that whenever DisplayPort Alt Mode is involved, connection will break after sleep or upon disconnect/reconnect.

    Interestingly enough, when running the High Sierra installer (via recovery mode) the issue is not there. So it's an issue with whatever drivers are installed in High Sierra itself.

    Anyone on here with a tMBP with Radeon 455 who does *not* have the issue on DisplayPort?
  3. mrlund macrumors newbie

    Feb 13, 2018
    Thanks for the very precise post and description. I am having this exact issue, with a 4K USB-C monitor (Acer H277HK) connected to a touchbar MBP 15" with the Radeon Pro 455 graphics card which also will switch on and off with a few seconds interval after waking from sleep. Only fix is to restart the mac.

    I don't use my 4K monitor that often, only for specific work that requires the pixels, and this is super frustrating.

    I'm sending my MBP in for service since the some keyboard keys stopped working. I might claim this as a fault too, and see what they say.
  4. ManuCH thread starter macrumors 6502a

    May 7, 2009
    Please let us know if sending in the MBP for service fixes the issue. If it does, I'll send in mine, too. If, however, this is an issue all MBPs have with those monitors, then I won't waste my time with it.
  5. mrlund macrumors newbie

    Feb 13, 2018
    UPDATE: While I haven't been able to spare my machine long enough to take it to service yet, I can confirm that using the USB-C to HDMI (I use the Apple AV dongle) "solves" the problem in both MacOS and Windows 10 with bootcamp. Plugging / unplugging / sleep / wake etc the monitor behaves as you'd expect.

    Obviously this is not a fix, but just a workaround and we can't get power over USB-C etc. I guess you can't expect too much from a $2,500+ Apple device these days :-(

    I'll update again after service, but given this experience I'm afraid we know the answer already; it's unlikely to be a hardware issue, so they'll probably dismiss it.

    I wonder if anyone is having this issue with any of the Apple "sanctioned" LG 4k USB-C monitors?

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4 September 28, 2017