Apple Vision Pro is now available in the U.S.

External USB-C Monitor stopped working in macOS Sonoma

I've been using my LG Ergo 32un880 on my M2 MacBook Pro since the start and never had any problems. Now, in macOS Sonoma the Display completely stopped working in terms of is not being recognised at all anymore. Someone having the same issues or any solution?

MacBook Pro 15″, macOS 10.15

Posted on Sep 25, 2023 1:49 AM

Reply
Question marked as Best reply

Posted on Nov 8, 2023 6:50 AM

I had the same problem with my M2 Pro and LG HDR 4K after upgrading to Sonoma 14.2. Spoke to LG Support. They had me do a hard reset of the monitor - unplug the monitor, hold down the power button on monitor for 10 sec while unplugged, then plug monitor back in...and it worked!

30 replies

Dec 16, 2023 6:54 AM in response to scaledoctor

<< My current USB-C cable from the MacBook Air is around 2 m length. Do you think a shorter one could be the solution? >>


Yes, exactly that.


later versions of MacOS are more demanding in seeing error-free trasmisson.They ask the display if any transmission errors have occurred, and if they have, the display goes dark or its resolution is reduced.

Nov 8, 2023 8:46 AM in response to alexisrod1111

What I read into that is, "don't always assume that the Mac is the problem -- it is also possible your display is confused, and in a funny state."


In the case of the Apple Studio display, that is frequently the case. When the Studio Display misbehaves, it needs a timeout. Disconnect all power and cables and let it sit by itself for a quarter hour. (Facing it into the corner or moving it to the 'naughty stair' is optional.)

Dec 16, 2023 1:34 AM in response to Grant Bennet-Alder

I made a small diagram of my setting which worked flawlessly before the update. The KVM switch (3 inputs: DP,DP,USB-C) has an own power supply, my monitor a resolution of 3440x1440. After the update the MacBook Air is not detecting/activating the external display for some reason anymore. My current USB-C cable from the MacBook Air is around 2 m length. Do you think a shorter one could be the solution?


Dec 20, 2023 8:52 AM in response to Tholitz_Reloaded

a proper USB cable to support a high resolution display on recent macOS is ONE METER in length or shorter. And it has the USB-C SuperSpeed PLUS icons on both ends or on a tag:



uncertified, unmarked cables are very often less than excellent quality. Cables 'shipped in the box' are often "lowest bidder" cables, and are just good enough to keep you from returning the display on the first day.


The FRONT USB-C ports on Mac Studio MAX (not Ultra) are NOT fast enough to run a high resolution display. They are explicitly limited to 10 G bits/sec maximum, with no ability to 'turn around' the inbound data paths for momentary outbound use to attain the required about 20 M bits/sec required..

Sep 25, 2023 7:39 AM in response to yoselm

LG Ergo 32un880 appears to be a "4K" display with

USB-C and

HDMI inputs.


HDMI is bandwidth-limited and trouble-prone at high resolutions.

to use an HDMI cable at that resolution on a modern Mac requires:

HDMI cables you want for HDMI-only Displays (higher resolutions than 720p TV sets) are marked as Certified with an anti-counterfeiting tag and are labeled:


"Premium High Speed HDMI cable" or that + "with Ethernet" --OR--

"Ultra High Speed HDMI cable" or that + "48G"


Cables with No Certification tags are good for your standard 720p TV set, and not much more.


Sep 25, 2023 8:12 AM in response to yoselm

<<. I've been using the cable that came with the monitor since I got it and it has been working perfectly ... >>


cables that shipped in the box are infamous for being just good enough to keep you from taking the device back to the store. if yours is not CERTIFIED, you need a cable that is CERTIFIED and has those markings, and is appropriately SHORT.


<<. ...before upgrading to macOS Sonoma... >>


Yes, but you changed something. Sonoma is not the same as the previous MacOS. Each successive version of recent MacOS has tightened the tolerances for what is acceptable for errors generated in data transmission to the display. Get a known-good CERTIFIED cable and that may solve your problems.

Sep 26, 2023 9:58 AM in response to yoselm

<<. Now I have to restrict my space because the cable can only be 1m? >>


The data rate used by a high-end, Hi-DPI, hi-color display is THE most intensive data stream produced in your Mac. It is Faster and more unrelenting that the data read from disk. The data rates are approaching the physical limits of switching speeds of electronic devices, so cable-lengths are limited.


if you reduce those requirements, such as by reducing the resolution of your display, you can use a longer cable.

Nov 18, 2023 2:23 PM in response to yoselm

I'm having the same issue with my Phillips 32 inch widescreen monitor. Everything was working perfectly with my monitor. I upgraded to Sonoma and the monitor did not work. I was using a TRIPP-LITE adapter connected through HDMI. Connection through the TRIPP-LITE does not work through HDMI nor USB-C. When I plug my computer into the AC adapter and use the USB-C adapter, it works. If I try to run my monitor off battery, it seems Sonoma doesn't have enough power to display both monitors. This means I cannot use USB 2.0 adapters (as all thunderbolt/usb-C ports are being used) with two displays. Apple - please fix this. Unplugging my monitor to power my external hard drive is a joke!

External USB-C Monitor stopped working in macOS Sonoma

Welcome to Apple Support Community
A forum where Apple customers help each other with their products. Get started with your Apple ID.