User profile for user: denzik
denzik Author
User level: Level 1
4 points

Macbook Pro M2 MacOS 15.4 - Not detecting and not sending picture to External Monitor

I've unplugged my monitor for a thunderstorm, and after such the next day I plugged it in and the Macbook Pro M2 computer has now stopped sending a picture to the external monitor and "detect displays" no longer recognizes it. I know that the Monitor works because I've plugged it into another Macbook that I have and it correctly displays screen picture on the external monitor when attached to that second device. It is also not a cable issue as that has been working previously and with the second macbook.


Here's what I have done to try and get it to work:

  • I've rebooted the machine while connected to the monitor
  • I've rebooted the machine while not connected to the monitor then plugged it in.
  • I've rebooted the machine while not connected to the monitor and the monitor power unplugged then connected both the monitor to power and to the macbook via USB-C cable


I've even tried going through these steps, and infact I had this issue previously and these steps worked once a few months ago, but after the latest incident they still do not work after trying a few times

macOS Sequoia 15.3 wont let me detect my … - Apple Community


However, attempting to go through these same steps again has not worked. After a restart once i've removed the .plist file... the Monitor will display a nearly full gray picture but nothing actually related to the desktop or extended screen. When I attempt to unplug and plug back in the monitor again it goes back to just all black screen as if it were slept, but no picture. Additionally there is nothing recognized after I attempt to do a "detect displays" by holding option on the displays menu to replace the night-shift button.


I'm kind of at a loss here... I cannot reset PRAM as the m2 chips don't have that ability.


I'll continue to try and detect and unplug and try every which combination, but nothing seems to be working. I'm also updated to Sequoia 15.4 and that has not yielded any difference.

MacBook Pro 16″, macOS 15.3

Posted on Apr 2, 2025 7:38 AM

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User profile for user: denzik
denzik Author
User level: Level 1
4 points

Apr 2, 2025 7:33 PM in response to Grant Bennet-Alder

Monitor Make and Model:

  • Samsung - LC49G95TSSNXZA


I'm using the USB-C -> Display Port connection.


There are no adapters, it is a direct USB-C to Display port into the back of the monitor, and there are no docks present.


The Cables are from Maxonar. I bought them to work with the previous Laptop but recently got a new work computer and they have worked in the past with no issues until the Sequoia Updates.


The Amazon Product Description from when I ordered them:

"USB C to DisplayPort VESA Certified, Maxonar 8K 60Hz Type-C to DP Cable 6.6FT/2M(4K 60Hz 144Hz 120Hz 2K 240Hz) 32.4Gbps 1.4 HBR3 Alt Mode Adapter for 2021 MacBook Pro M1 Mac Mini, XPS 15 Grey"

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User profile for user: Grant Bennet-Alder
Grant Bennet-Alder
User level: Level 10
135,865 points

Apr 3, 2025 6:54 AM in response to denzik

  • that Samsung - LC49G95TSSNXZA

appears to be a 5120 by 1440 display, like the top half of a 5K display, with 10 bits/color


interfaces include:

ONE HDMI 2.0

two displayPort 1.4


based on standard timing, it does not appear possible to run a 5K display higher than 30 Hz on a single DisplayPort cable, and to get that result, the DisplayPort cable would meed to be ONE meter or shorter.


based on standard timing, HDMI 2.0 could run a 5K display at 30 Hz with 10 bit color -- possibly higher with 8 bit color.


To get that display to work in a standard way on a modern Mac, the device-maker SHOULD have included a HDMI 2.1 or Thunderbolt interface to get high enough data rates.


You can instead connect with TWO cables, each carrying the right or left half-display, and put them back together with the display's Picture-By-Picture feature (cousin of Picture-In Picture). Users report this works great on the Mac.

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User profile for user: denzik
denzik Author
User level: Level 1
4 points

Apr 3, 2025 9:11 AM in response to Grant Bennet-Alder

Thank you so much for assisting with this. I'm super confused though, because I have been able to run the monitor with this same macbook and same cable for almost 2 years.


The monitor was purchased in 2021 and i've been using it with this exact setup since May of 2023.


So something has changed recently with the MacOS Sequoia. Up until approximately 2 days ago it was working perfectly fine.


I can attempt to try and purchase new cables, but I'm just confused all off a sudden why this has stopped working. I'm definitely not an expert in this area though. The cables do work with my Intel 2019 MBP 16-inch.

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User profile for user: denzik
denzik Author
User level: Level 1
4 points

Apr 3, 2025 12:21 PM in response to Grant Bennet-Alder

Sequoia 15.2 Was definitely working. It had been working even on 15.3 for I believe up until a few days ago. I was able to removed the .plist file for displays and it was able to work, but while on 15.4 it's not been working. The screen goes gray, and if i unplug it it then goes black.

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User profile for user: denzik
denzik Author
User level: Level 1
4 points

Apr 4, 2025 2:25 PM in response to Grant Bennet-Alder

So if i use 2 USB-C Thunderbolt Ports to Display Port on the Mac... with 2x 3.3ft(or 1m) cables


Then these 2 short cables can be used with PbP to perhaps get the monitor to work?


You believe it is the Mac and MacOS being stingy with the cables and no video loss that is the problem?


Want to make sure I understand the potential theory before getting two cables off Amazon.



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Macbook Pro M2 MacOS 15.4 - Not detecting and not sending picture to External Monitor

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