MacBook M1 Pro fails to use two external monitors, while it should

Question

AZH2023 Author

Level 1

4 points

MacBook M1 Pro fails to use two external monitors, while it should

Hi, my MacBook M1 Pro can use only one external monitor, but I know it should be able to use two. Details are as follows:

MacBook M1 Pro (14-inch, 2021)
macOS Monterey
DELL S2722QC display (27-inch, 3840 x 2160, connected via USB-C)
LG 25UM58 display (25-inch, 2560 x 1080, connected via HDMI)
Either one of them can be detected, depending on which one is plugged to the laptop first. But they cannot be both detected together at the same time.

Thanks!

MacBook Pro 14″, macOS 12.6

Posted on Nov 2, 2023 9:12 AM

Reply

Answer 1

AZH2023 Author

Level 1

4 points

Nov 2, 2023 12:16 PM in response to Grant Bennet-Alder

Hi, thanks for the very detailed explanation! I've just figured out the issue's not from the cables. After a reboot the system can now connect both monitors. It looks to be some unknown issue in the OS or something like that.

Thanks again for helping out!

Reply

Answer 2

Nov 2, 2023 11:20 AM in response to AZH2023

USB-C cables to support displays at up to 4K resolution should be certified USB-3.1 SuperSpeed+ cables or better, and limited to one meter total length.

They should be marked with this logo or better:

To attain the required about 18 G bit/sec speeds, these same cables momentarily 'turn around' the inbound data lanes and use them for all outbound data part of the time.

"shipped in the box" cables without any certifications or logos are notorious for being just good enough to keep you from quickly returning the product to the store.

Reply

Answer 3

Nov 2, 2023 9:41 AM in response to AZH2023

EXACTLY what cables, adapters and Docks are in use to make the connection to each display? please mention EVERY item. Also, about how long are these cables?

Reply

Answer 4

AZH2023 Author

Level 1

4 points

Nov 2, 2023 11:07 AM in response to Grant Bennet-Alder

Hi, thanks for offering help! More details are as follows:

A normal USB-C cable, 1 meter long, connects DELL S2722QC directly to MacBook Pro's USB-C port on the left side. No adapter/dock in between.
A normal HDMI cable, 1.5 meter long, connects LG 25UM58 directly to MacBook Pro's HDMI port on the right side. No adapter/dock in between.
No other external devices are connected, just these two monitors.

Hope this information helps! Thank you so much!!

Reply

MacBook M1 Pro fails to use two external monitors, while it should

Similar questions