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I recently bought a MacBook Pro 13-inch 2017 and an LG Ultra HD (27UD88) 27" display. Before buying the display I researched a bit and found no issues in relation to the MacBook Pro.

However, after attaching the screen via the USB-C cable that came along with the display, I only have the option of a 30hz refresh rate.

I've Googled this without finding much - it seems like no one else is having this problem. From a result, I've also learned that my "Display" page in "System Preferences" looks slightly different than a screenshot from an article.

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  • Why change the tag from 4K to 5K? This LG monitor is 4K. 3840p.
    – benwiggy
    Jun 8, 2020 at 11:33
  • I think you're right. I was tricked by this in the system report: imgur.com/euIRJxB. Do you have an idea why it shows like so?
    – Thomas Jensen
    Jun 8, 2020 at 12:42
  • Weird. If you screenshot the whole screen (shift Command 3), what's the dimensions on the .png?
    – benwiggy
    Jun 8, 2020 at 12:49
  • According to "get info": 5120 × 2880. From the "Displays" tab: imgur.com/3nZLfLs.
    – Thomas Jensen
    Jun 8, 2020 at 13:37

2 Answers 2

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I got it working. I'm not sure exactly how, but here's what I tried, in the order of what I believe fixed it:

  1. Enable DisplayPort 1.2 in screen configuration
  2. Reverse the USB-C cable
  3. Set "Ratio" to "1:1" in screen configuration (I've since tested this and switching it back had no negative effect)

(3) was recommended by a user in a forum thread.

Update 2018-01-29

I've since experienced the problem once more, without changing any settings. Attaching/detaching the cable fixed it.

Update 2018-05-06

After the most recent MacOS update (10.13.4) it no longer downgrades to 30hz, instead, it never comes on. If the cable is dettached, the computer crashes and has to be booted. So far, the only solution I know of is restarting the computer, which works 50 % of the time, and if not, reattach the cable (it usually won't crash after a restart).

This happens after screen sleep and detaching/attaching.

Update 2018-12-13

In this third evolution of the problem (MacOS 10.14.1) the computer no longer crashes. Roughly 9/10 times it will display in 30hz/horrible resolution and all I have to do (sigh) is detach/attach the cable until I hit that 1/10 where it works. It's a daily 5 minutes routine for me.

This setup (MacBook Pro 13" 2017 w/o touch + 27UD88-W) is not recommendable to anyone.

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I had same problem with any HDMI cable. My solution was: MacBookPro 2017 thunderbolt out > thunderbolt in on a hub > Display Port cable out from hub > Display Port cable into back of LG monitor. Looks beautiful. And when I bring up Apple's display system prefs, the LG shows the same window with 5 scaling options that appears on laptop itself. Refresh rate not displayed but it's smooth and fast.

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  • Does the hub charge the computer as well? If so, which hub specifically do you have?
    – Thomas Jensen
    Oct 28, 2018 at 14:47

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