M4 MacBook Pro external monitor blanks occasionally

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M4 MacBook Pro external monitor blanks occasionally

I'm having an issue with using an external monitor via USB C. I have a Nov 2024 M4 MBP Sequoia 15.7.1 that I exclusively use an external monitor on. Occasionally, the screen will go blank for about 1-2 seconds before re-appearing again. This is not the laptop going to sleep, as it's plugged in and it will happen when I'm actively typing. I can only temporarily fix the issue by unplugging the external monitor and then plugging it back in, but the issue will come back after a few hours. It's incredibly distracting.

Here is my setup: 4K external monitor is connected via an 8K Displayport cable to an 8K Displayport switch. Connected to the switch on one side is another 8K Displayport cable connected to my desktop, and on the other side of the switch it's connected to a Displayport to USB C cable that connects to my MBP. I don't think this is a noise issue on the switch because I always have my desktop off while using my MBP, and when I use my desktop my MBP is still running and I've never had any display issues on my desktop (Linux). For that reason, I also don't think this is an issue of the Displayport switch being faulty either since I use my desktop for hours at a time with no issues at all.

Has anyone else ran into this issue? Is there a fix for it? Or some display specific logs to check?

Posted on Nov 21, 2025 1:56 PM

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Answer 1

Nov 21, 2025 4:23 PM in response to atommisssing

The length of a DisplayPort cable for most stable operation is ONE meter, maximum.

If your Switch really is just a Switch and does not contain Re-Driver electronics, that would mean the SUM of lengths all the cables between the Mac and the Display would need to be no longer than ONE meter.

if your Switch is actually a Re-Driver, then the sum of the lengths of the cables INTO the Re-Driver should be one meter or less, and the sum of the lengths of the cables from Re-Driver to display should be should be one meter or less.

The Apple standard for its built-in hardware-accelerated displays, makes them suitable for full-motion video for production/display of cinema-quality video with NO dropped frames, and NO dropouts or partial-blank scan lines due to memory under-runs or Transmit errors due to low-spec cables.

Many readers have found that their cables are too low-specs or too long for reliable operation.

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