I have a Samsung 28" U28E590 4K Display and a 13" MacBook Pro with Touch Bar (Intel Iris 550 1536 MB Graphics). I have a dongle for HDMI output.

The problem is that the external monitor flickers, displays white noise and sometimes cuts out completely. I've tried SMC reset and buying a new HDMI cable, but the issue persists.

How do I resolve the issue?

  • 2
    Solution: Using a DP cable + Mini DP to USB-C dongle
    – Greggless
    Commented Jan 24, 2017 at 12:32
  • 2
    Ugh. Apple support for external monitors is so terrible. How can the solution be: just buy another dongle. To Apple: if it doesn't work using HDMI, please just say it doesn't work, that way people won't spend 200$ buying the wrong cables/dongles.
    – levesque
    Commented Aug 16, 2017 at 18:05
  • I know, terrible. Now the screen has stopped working completely after an OSX update! It turns out Samsung screens don't play nicely with MBPs
    – Greggless
    Commented Aug 21, 2017 at 11:51
  • Update: USBC-Displayport has issues on the 2018 MBPs, I also get intermittent flickering with HDMI on Dell Ultrasharps. I hope an update fixes these issues but apple will likely just release their own monitor for $1K again and forget about everyone else. apple.stackexchange.com/questions/332557/… Commented Aug 16, 2018 at 19:31
  • 1
    I had the same problem for long time. Just now I found that if I go to display settings and change the resolution of the external screen, the problem goes away (you can change the resolution back to its old value). Maybe the change of resolution will trigger some event in the OS internally and update some configurations to get the monitor synchronised. I think this worths a try if you have the same problem.
    – doraemon
    Commented May 7, 2020 at 0:43

14 Answers 14


I've had a support case at Apple for over a year about this issue. They finally answered that it's a software issue and they are looking into it.

We have spent a lot of money in our business on original adapters and good technics to have a good setup. Several of our MBPs with USB have this flickering problem on 1 of the 2 screens (always the screen you attached last).

I really hope that Apple can find this seriously soon or they will probably lose more customers. We are not very satisfied. After all, we have spent lots of money at Apple to get this sorted with no result more than an answer 1 year after - the answer "it's an Apple software problem".

  • 1
    I'm using a Dell external monitor and had the same issue. My issue was solved when I changed the screen refresh rate to 50 Hertz and the resolution to 1080p. Commented Sep 15, 2020 at 3:58
  • They will probably lose more customers. I only got a MBP because I can't develop for iOS without one, which is a shame because only a small percentage of our users actually is on iOS. Luckily dual booting is not a problem, but a HP Envy for example is just so much nicer! It's such a beautiful sleek machine and for the price of a 2 year old mac. I don't get Apple even still exists at all.
    – ThaJay
    Commented May 17, 2022 at 10:27

I just had this issue with a 2016 MBP and a Samsung 28" U28E590 Display. Tried a bunch of things, but what seemed to work was switching the monitor to use to HBR1.

The setting was in the monitor's menu under System -> DisplayPort Ver.

As soon as I switched it, the intermittent flickering stopped.


I have the same 4k monitors (Samsung 28" U28E590 Display) and just purchased a 2017 MBP 15" 2.9 GHz Intel Core i7. I experienced rapid flickering when hooking up HDMI to the Apple Multiport Adapter (via it's HDMI port), after a bit of research on that monitor I found that it's best supported by the DisplayPort and that the HDMI was extremely unreliable with most new MBP's. I then went out and purchased a USB-C to Display port adapter (you should have gotten a DisplayPort cable with your monitor) and voila! No more flicker. The picture quality even seems a bit better. I am not ordering 2 new USB-C to DisplayPort cables which, based on the test with the adapter, should work.

Here is what I've ordered: https://www.amazon.com/DisplayPort-ITANDA-Thunderbolt-Compatible-ChromeBook/dp/B074GVQBY2/ref=sr_1_1_sspa?ie=UTF8&qid=1513745117&sr=8-1-spons&keywords=usb-c+to+displayport&psc=1


Have you checked for software updates from the App Store since the first time you connected the expensive dongle for HDMI output?

  • After connecting for the first time there is often a firmware update that is necessary for the dongle to function correctly

You could try a PRAM reset on the shiny new MacBook Pro 13" (if you haven't already).

You could try booting into - and back out of - Safe Mode.

Have you ensured the expensive dongle for HDMI output isn't defective?

  • You could test with a different display like a TV to see if the issue still occurs. (And if you happen to have a second Mac other than the shiny new MacBook Pro 13" hanging around for testing, that would narrow it even further!)

Have you ensured that the expensive dongle for HDMI output isn't incapable of supporting such a high resolution?

  • To test you could try lowering the resolution from 'System Preferences > Displays > Display'

Have you tried installing/reinstalling the shiny 4k monitor drivers?

If issue persists, I have a few more questions.

Last but not least, a little shiny bird told me that 4K displays have to be configured for 60Hz to function correctly. If it's being forced into any other refresh rate (like 30Hz), that could be the problem.

  • Thanks for your shiny response! :) Ok, so let's answer these: - Firmware for expensive dongle is up to date - I have done a PRAM and SMC reset to no avail - I've enabled and disabled safe mode, I think, are you referring to SIP mode? - Currently unsure on the dongle's reliability - I have another MBP 13" 2015 that I was using that did not have a flicker problem - I will test on another TV to see what happens - Firmware drivers for the Samsung screen are Windows only -_- - Flickering happens randomly at any point, not dependant on intensive graphics usage
    – Greggless
    Commented Jan 20, 2017 at 14:51
  • Sorry for the formatting. The external monitor is being output at 30hz, which sucks and i've tried a whole bunch of things to get it to 60hz with no joy!
    – Greggless
    Commented Jan 20, 2017 at 14:53
  • 1
    Unfortunately in Sierra the option to change the refresh rate on a per-display basis is no longer an existing feature. In previous OS X versions when you connected a display and went to 'System Preferences > Displays > Display' selecting certain resolutions would allow you two toggle the refresh rate between 30hz and 60hz, but this is no longer the case. I'm not sure Apple will be of much help as this isn't a bug, but a removed feature. I believe the thought process behind removing it was that the OS was supposed to be smart enough to automagically choose the correct refresh rate on its own.
    – NYKg
    Commented Jan 20, 2017 at 18:53
  • 1
    ...But clearly it doesn't always get it right! From my research online I see that some people have found a couple of 3rd party solutions such as something called cscreen (a Terminal app - pyehouse.com/cscreen) or Switchresx (seems a little more user friendly/easier to use - madrau.com); both of which require you to install something called 'Mac Pixel Clock Patcher' first (details founds in this answer to another question: apple.stackexchange.com/a/232872/220050)
    – NYKg
    Commented Jan 20, 2017 at 19:03
  • 1
    One final comment - Safe Mode is actually something different than SIP mode. Apple quote: "Safe mode is a way to start up your Mac so that it performs certain checks and prevents some software from automatically loading or opening." (including non-required kernal extensions) To boot into Safe Mode simply: Start or restart your Mac, then immediately press and hold the Shift key. The white Apple logo appears on your display. Release the shift key when you see the login window. To get out of Safe Mode, just restart the Mac without holding any keys down.
    – NYKg
    Commented Jan 20, 2017 at 19:11

I had the same issue on different systems and could fix it by resetting the SMC:

  • Connect the computer to the power supply (MacBooks)
  • Turn the computer off
  • Press and hold the Shift + ctrl + Option + Power buttons for 3 seconds
  • Release all buttons at the same time
  • On MacBooks, the power plugs light will change to let you know it worked out
  • Start your system normally

After testing in three different monitors and a couple more cables got it working upgrading my miniDP-DP cable to a HBR2 ("High Bit Rate 2") compatible cable. StarTech.com MDP2DPMM1M

  • Are you aware of any incompatibility between Samsung screens and Macbooks? My Screen has completely stopped working since a recent MACOS update.. The Macbook detects the screen, and resizes its screen based on the mirroring preset I had set up previously. But the screen just wont display anything and cycles through the channels..
    – Greggless
    Commented Aug 2, 2017 at 13:36

For my MBP, I bought the USB-C - Display Port -cable and there is no flickering, HDMI goes crazy with flickering.


I've had similar issues for months. First on my MacBook (2016), then on my MacBook Pro (late 2018).

I even returned a couple UHD monitors to the shop until I found one (LG brand) that didn't flicker and kept it at that. Only when I got yet another UHD monitor in another location, without the ability to return it (and it was pricey) did I have to find a solution. SMC reset and HDMI cable swap did not work.

The only solution that has ever worked for me is ordering a USB-C to DisplayPort cable and ditching the HDMI dongle and cable. Works perfectly now. Reference: Startech CDP2DPMM6B.


It looks like this is a very old problem with Macbooks Pro, I have a MB Pro 13" mid 2012, and the same is happening right now, like ARM44 tells in this link https://discussions.apple.com/message/32182556#message32182556:

I'm having the same issue. . .brand spanking new MacBook Pro 13' with touch bar connected via the Apple USB-C digital AV multiport adapter and HDMI cable to an equally brand spanking new Dell U3415W 34' curved display. The only way I've been able to get the Dell display to work without flickering is:

  1. Set the Dell display refresh rate to 30 hertz.
  2. Keep the lid of my MacBook open and set the Dell as the primary screen (move the top menu bar).

As soon as I close the lid. . .flickering and/or permanent black out. This is obviously a universally encountered issue by any new MacBook owner trying to connect to a 4K or better external display. I've tried all of the other suggested solutions (resetting PRAM, etc. . .) as well. While not ideal, it has at least enabled me to be able to use my external display while waiting for Apple to get around to fixing the issue.

in my case I have to keep the lid open to work without problems with an external monitor. I hope it helps.

  • Welcome to Ask Different! We try to refrain from link only answers, as they decrease readability and are susceptible to link rot. Can you add any relevant text from the link to the body of you post?]
    – JMY1000
    Commented Jan 20, 2018 at 23:30
  • You're right, what do you think now? :D
    – Mr. DMX
    Commented Jan 21, 2018 at 0:20

I used a HDMI cable HDMI from Samsung and the flickering went away.

I have a 13" MacBook Pro 2017, Core i5 256GB No Touch Bar, Intel Iris Plus Graphics 640 1536 MB graphics, Samsung UE510 UHD (LU28E510DS/ZA) running @HDMI 3840x2160 67.4kHz 30Hz. The display is connected with a Apple USB-C Digital AV Multiport Adaptor.

  • Thanks for the reply, therein lies my issue: Working on a large screen @ 30hz is a real pain in the neck! Getting 4K @ 30hz is no problem, it's the 4K @ 60hz that I am hunting for
    – Greggless
    Commented Apr 16, 2018 at 13:27

I experience the same issue with my Dell UP2716D monitor after upgrading my MacBook pro retina to high seirra and tried different methods also couldn't work, finally I changed the resolution setting rather then using the default for my external monitor and it all back to normal again (also, my usual setting is to turn on the the MacBook pro screen with mirror display selling) hope this could help someone facing similar problem.


I had the same issue and found a lot of confusing and complex suggestions on this post. My solutions turned out to be simple. I recently purchased a MacBook Pro (2018) and a large 4K Samsung external monitor. The Monitor was connected using an HDMI cable, converted to USB C using the Apple multiport adapter. The screen kept flickering when connecting them.

What worked for me was quite simple. I purchased a new HDMI to USB C cable that supports 4K/Ultra HD display (mine was from UGreen, it supported 4K @60hz - quite cheap as well) and it now works like a charm. I guess the Apple adapter did simply not handle the data rate between the computer and the screen...


Thanks folks for these answers. Flickering on my 2019 Mac Book Air does indeed stop with a USB-C to DisplayPort. It’s sad that the expensive Apple Multi-port A\V don’t support HDMI reliably.

If anyone finds a solution to take the two USB-C’s on the 2019 MacBook Air and get Pass-through charging, Ethernet, and two USB-A ports please post. So may docks have issues with the Power Distribution.

Till then I will be plugging and un-plugging and using WiFi.

I actually suspect Power distribution is the issue with the Apple A\V Adapter.


I had to change the color profile of my external monitor to "sRGB IEC61966-2.1" and the flickering and weird lines/artifacts on my external monitor went away.

Settings -> Displays -> Click on your external monitor to select it -> Change the color profile to "sRGB IEC61966-2.1"

You must log in to answer this question.

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