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8 points

M1 Macbook Pro - Dell External flicks from on to black, back and forth

Have seen other people out there with the same issue - I have 2 M1 Macbook Pro's at my house and they both do the same thing. Plug in my 2 new Dell S2721QS 4k monitors and immediately one of them will start flashing black and then come back, then black again and so on.


I am connecting these monitors using DP to USB-c cables into the USB-c ports on the machines directly.


I have tried swapping cables, no difference.

I also have a 2019 Intel Macbook Pro and the screens work perfectly for this machine everytime.


In order to resolve this issue, I keep having to adjust the display settings until the screen stops flashing, but this only works for a limited time, the next time I connect the screens or turn the computer on we are back to square one. I can also remove the cable and plug it back in a number of times, and eventually the screen stays on.

MacBook Pro (2020 and later)

Posted on Feb 16, 2022 1:41 PM

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User profile for user: Why Can't I sign in
Why Can't I sign in Author
User level: Level 1
8 points

Posted on Feb 18, 2022 3:55 PM

I had previously bought another DP to USB-c cable and had the same issue.


I have now realised that one of the monitors/cables seems to work everytime - so I swapped that cable to the other monitor and now that one works everytime. So even though I have tried 2 different DP=>USB-c cables on one monitor and had the same results, it seems both of those cables might have been not high quality enough.


I also tried a high quality HDMI cable and it is working.


Finally I tried the good DP => USB-c cable with a USB-c cable extender, and it stopped working. So it would seem that the quality of the cables is really important here, I am not sure of the specs, but if you come across this issue that might be your problem.

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User profile for user: Why Can't I sign in
Why Can't I sign in Author
User level: Level 1
8 points

Feb 18, 2022 3:55 PM in response to DonH49

I had previously bought another DP to USB-c cable and had the same issue.


I have now realised that one of the monitors/cables seems to work everytime - so I swapped that cable to the other monitor and now that one works everytime. So even though I have tried 2 different DP=>USB-c cables on one monitor and had the same results, it seems both of those cables might have been not high quality enough.


I also tried a high quality HDMI cable and it is working.


Finally I tried the good DP => USB-c cable with a USB-c cable extender, and it stopped working. So it would seem that the quality of the cables is really important here, I am not sure of the specs, but if you come across this issue that might be your problem.

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M1 Macbook Pro - Dell External flicks from on to black, back and forth

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