USB hub in external display works intermittently

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USB hub in external display works intermittently

I'm running an NEC EA271U external display with a MBP 2018 using the USB-C connection. I bought a separate cable that supports charging, 4K@60 Hz plus USB 2.0.

I've connected a mouse and a keyboard to the display's inbuilt USB hub. Now sometimes the hub doesn't work so that I only have an image but no input from mouse or keyboard. I haven't found a pattern so far, it can happen that I open the MacBook's lid while the USB-C cable is connected, the image works at the correct resolution but mouse and keyboard doesn't work.

Other times it works, I boot up and everything works fine. Most of the time it doesn't work to connect the display in clamshell mode, the mouse might respond but then the screen turns dark. So I connect the screen while the lid is open, everything works and then I close the lid and it's fine.

Anybody got any idea what it could be?

MacBook Pro 15”, macOS 10.15

Posted on Mar 5, 2020 12:20 PM

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Answer 1

Mar 5, 2020 12:27 PM in response to jost-s

Try booting into Safe Mode. When you do this, the OS does not load all the higher end graphics and other drivers for, nor does it load third party additions. It does file directory repair, maintenance and cleanup. So don't be surprised if your video looks odd. But once done and you've logged in, see how things behave in safe mode. Then just restart again normally because the tasks we're expecting to be done have been done. Reboot and see if the problem persists.

Use safe mode to isolate issues - Apple Support

What Safe mode does:

Verifies your startup disk and attempts to repair directory issues, if needed
Loads only required kernel extensions
Prevents startup items and login items from opening automatically
Disables user-installed fonts
Deletes font caches, kernel cache, and other system cache files

Restarting in Safe mode can often eliminate a problem or help identify the cause.

You can verify that you have started in Safe mode by clicking Apple menu  > About This Mac > System Report. Then find >Software< in the left column and look at >Boot Mode: Safe vs Normal< in the right pane.

Note– starting up in Safe mode could take 10 minutes or more. Be patient.

Does the problem persist while in Safe mode?

Restart your Macintosh and re-evaluate the issue.

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Answer 2

Mar 5, 2020 12:44 PM in response to jost-s

Follow up–

Here's a link to an Apple Support document regarding using external displays on the 2019 MacBook Pro. While not specific to your particular MBP model, it may be close enough that you'l find something useful.

Use an external display with your MacBook Pro - Apple MacBook Pro Essentials

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Answer 3

jost-s Author

Level 1

9 points

Mar 6, 2020 12:15 AM in response to D.I. Johnson

Thanks a lot for your suggestions. I've booted into Safe Mode and there the issue was the same.

The external screen comes on but the USB peripherals aren't working. I noticed now that power cycling once or twice will resolve it, mouse and keyboard work after switching it back on while connected.

The other problem, as I said, is that when the MacBook's lid is open and the mouse works, the external screen will often turn dark. Shutting the lid resolves this.

I've also reset the PRAM. It's mysterious to me, because generally it's working, just not always as it should. Any other ideas?

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USB hub in external display works intermittently

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