User profile for user: aselwood
aselwood Author
User level: Level 1
11 points

External Monitor Goes Black and Comes Back

I have a new MacBook Air M2 - and am using a USB-C dongle (that provides HDMI, 3xUSB, and wired ethernet) and the external monitor goes black and comes back randomly about every 10-30 seconds. it stays black for about 5 seconds.

The same dongle (with same connections) works fine with Windows laptop.

Have tried same Macbook with different dongles, different monitors, different cables, and problem is the same (although interval sometimes is longer)

MacBook Air, macOS 12.6

Posted on Oct 20, 2022 7:00 PM

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User profile for user: aselwood
aselwood Author
User level: Level 1
11 points

Oct 25, 2022 4:53 PM in response to ArmMan1016

Hello again...

Surprise

I tried resetting the NVRAM, but honestly not sure if it worked.

Checking the documentation - Reset NVRAM on your Mac - Apple Support .. it says you can't do this on Apple Silicon - and this is an M2 Macbook Air.

Anyway - after trying Option-Command-P-R it rebooted, and the external monitor on HDMI is still flashing.

Interesting ... Just tried my son's computer monitor .. with USB-C to DP cable .. and no flashing. It's 2560 x 1440 @ 144Hz .. so I took the USB-C to DP cable to my monitor, and no flashing? it's running 3440 x 1440 @ 75Hz and is working!?


I'm confused - I could've sworn we tried the USB-C to DP cable earlier - and it didn't work.. but now it does...

So .. I'm calling it solved! Still interesting that over HDMI it didn't work (with Mac) but did work (with Windows) but over DP it does.




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User profile for user: Lager1
Lager1
User level: Community Specialist

Oct 22, 2022 5:24 PM in response to aselwood

Hi aselwood ,



You have tried some great steps to rule out an issue with the dongle, cables and the external monitors.


So, perhaps this is software related. Let's try to narrow this down and isolate it more by testing in safe mode and a new user account.


Safe mode prevents certain software from opening and completes great checks on startup. More information on starting to safe mode and steps to take after starting there can be found here: How to use safe mode on your Mac - Apple Support


  1. "Shut down your Mac.
  2. Turn on your Mac and continue to press and hold the power button until you see the startup options window
  3. Select your startup disk, then press and hold the Shift key while clicking “Continue in Safe Mode”.
  4. Log in to your Mac. You may be asked to log in again."



If the monitor goes black after the steps from safe mode, create a new user account (administrator) to see if the behavior happens there. This will let us know if it is system-wide or something within your user account: Set up users, guests, and groups on Mac - Apple Support


Delete a user or group on Mac (to remove the test account once completed)


Let us know what you find


Cheers!


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User profile for user: ArmMan1016
ArmMan1016
User level: Community Specialist

Oct 24, 2022 3:06 PM in response to aselwood

Hello again aselwood

,


Thanks for that information. Now we'd like to have you try resetting the NVRAM, as this can help with most display and resolution issues. Find the steps in the steps in the Apple Support article: Reset NVRAM on your Mac - Apple Support


"How to reset NVRAM


  1. Shut down your Mac.
  2. Turn on your Mac, then immediately press and hold these four keys together: Option, Command, P, R.
  3. Release the keys after about 20 seconds, during which your Mac might appear to restart. For example, you might hear a startup sound more than once, or see the Apple logo more than once.
  4. When your Mac finishes starting up, you might need to adjust any system settings that were reset."


Let us know the outcome, and we can go from there if needed.


We look forward to hearing back from you. 


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User profile for user: aselwood
aselwood Author
User level: Level 1
11 points

Oct 24, 2022 2:40 PM in response to Lager1

Hello Lager1

so there was no change when I went into safe mode but here's a new thing I learned.

I tried connecting dongle HDMI to a HDTV (1920x1080) and it worked... no flashing

I then connected dongle HDMI to a 4kTV (3840x2160) and it worked ... no flashing

I also stole a USB-C to Displayport cable from my son (so no dongle .. straight from the macbook to the computer monitor) and it's flashing

My computer monitor is 3440 x 1440 (Viewsonic VG3448) .. is that an unsupported resolution for mac?

remember - same dongle, HDMI cable, and monitor - when connected to my Windows 10 laptop work fine - no flashing.


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External Monitor Goes Black and Comes Back

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