User profile for user: net-engineer6
net-engineer6 Author
User level: Level 1
4 points

MacBook M4 Pro Dual Monitors Not Working

I have 2x 4k monitors (MSI MAG 274UPF E2) that I'm trying to connect to my M4 Pro MacBook. I've tried various configurations (see below) and can only get one external monitor to display at a time. If both monitors are connected and I disconnect the active one, the inactive one will turn on and start working. I used to have an M1 Pro MacBook that worked just fine with these monitors at 4k60hz. In Display settings only one monitor shows at a time. Using detect displays from settings doesn't change anything. Only one display shows up at a time in system information.


Configuration #1 (Preferred, worked perfectly on M1 Pro)

Monitor 1 (DP) connected to CalDigit TS3 Plus (DP port) via DP cable. (4k60hz)

Monitor 2 (HDMI) connected to TS3 Plus (TB3 port) via HDMI-to-USB adapter with HDMI cable. (4k60hz)

TS3 Plus (Computer port) connected to MacBook Pro (TB5 port) via TB3 cable.

(Only one monitor works at a time and it's random which one comes up, resolutions I saw one at a time are listed above)


Configuration #2

Monitor 1 (DP) connected to CalDigit TS3 Plus (DP port) via DP cable. (4k60hz)

TS3 Plus (Computer port) connected to MacBook Pro (TB5 port) via TB3 cable.

Monitor 2 (HDMI) connected directly to MBP (HDMI) via HDMI cable. (4k144hz)

(Only one monitor works at a time and it's random which one comes up, resolutions I saw one at a time are listed above)


Configuration #3

Monitor 1 (HDMI) connected to TS3 Plus (TB3 port) via HDMI-to-USB adapter with HDMI cable. (4k60hz)

TS3 Plus (Computer port) connected to MacBook Pro (TB5 port) via TB3 cable.

Monitor 2 (HDMI) connected directly to MBP (HDMI) via HDMI cable. (4k144hz)

(Only one monitor works at a time and it's random which one comes up, resolutions I saw one at a time are listed above)


Configuration #4 (Trying to rule out TS3 Pro Dock)

Monitor 1 (HDMI) connected directly to MBP (HDMI) via HDMI cable. (4k144hz)

Monitor 2 (HDMI) connected directly to MBP (TB5 port) via HDMI-to-USB adapter with HDMI cable. (4k60hz)

(Only one monitor works at a time and it's random which one comes up, resolutions I saw one at a time are listed above)


Configuration #5 (Trying to rule out TS3 Pro Dock)

Monitor 1 (HDMI) connected directly to MBP (HDMI) via HDMI cable. (4k144hz)

Monitor 2 (USB-C) connected directly to MBP (TB5 port) via TB3 cable. (4k144hz)

(Only one monitor works at a time and it's random which one comes up, resolutions I saw one at a time are listed above)


Any suggestions on what may be wrong or how this can be resolved?

MacBook Pro 14″, macOS 15.5

Posted on Aug 5, 2025 10:27 AM

Reply
Question marked as Top-ranking reply
User profile for user: Grant Bennet-Alder
Grant Bennet-Alder
User level: Level 10
138,827 points

Posted on Aug 5, 2025 12:20 PM

two more items that complicate your experiments:


The Mac does not rely on Windows-like side-loaded "Drivers" which are actually packages of resolutions and settings for a specific display. Instead, it goes straight to the immutable source -- it asks the display itself.


To get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display. "No signal detected" is generated by the DISPLAY, not by the Mac.

 

This query is only sent at certain times:

• at startup

• at wake from sleep — so momentarily sleeping and waking your Mac may work

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• hold the Option key while you click on the (Detect Display) button that will appear in Displays preferences (from another display)


the second:


When a modern Mac detects a transmit error, it reacts by either dropping the data rate, or disconnecting the display.


DisplayPort cables are strictly length limited to assure that no signal attenuation will produce data errors.

ONE meter maximum for DisplayPort cables

ONE meter maximum for USB-C cables used for displays

0.5 meters maximum for ThunderBolt-3 and -4 cables, and -5 cables used as if they were the older ones.

0.5 meters max

View in context
25 replies
User profile for user: net-engineer6
net-engineer6 Author
User level: Level 1
4 points

Sep 9, 2025 01:02 PM in response to Grant Bennet-Alder

I would be perfectly okay with 4k 60hz on both displays. The refresh rate is the least of my worries -- ****, I'd even take 30hz if I could use both displays at the same time.


So, lets say that thunderbolt 3 cable can't support the two displays (still odd that it worked on M1 pro chip, but I see what you're saying about the newer chips supporting HDMI 2.1 -- although still weird that "backwards compatibility" doesn't seem to be a thing in that regard...). Why then can't I have one display connected via thunderbolt port and one connected directly to HDMI and have them both work at the same time (completely removing the caldigit from the equation)?

Reply
User profile for user: net-engineer6
net-engineer6 Author
User level: Level 1
4 points

Sep 9, 2025 03:10 PM in response to Grant Bennet-Alder

Unfortunately, that setup (display 1 connected directly via HDMI cable and display 2 connected via thunderbolt) still only shows one display at a time.


I have an Ultra High Speed HDMI cable that is 1.5m in length and a Thunderbolt 3 cable that is 0.5m in length.


I deleted the suggested preference list files and restarted but, still, only one display works at a time.

Reply
User profile for user: net-engineer6
net-engineer6 Author
User level: Level 1
4 points

Sep 10, 2025 12:08 PM in response to Grant Bennet-Alder

I showed all the resolutions and I see that 1920x1080 is already selected... when I looked at system information it was the same as my previous reply.


The only way to get system information to show a different resolution was to change it to 1280x720. This is what I saw in system information after doing that:


MAG 274UPF E2:

Resolution: 2560 x 1440 (QHD/WQHD - Wide Quad High Definition)

UI Looks like: 1280 x 720 @ 60.00Hz

Mirror: Off

Online: Yes

Rotation: Supported


My display still showed that it was using 3840x2160. Only one display still worked at a time after this.


It would be very difficult to work if the setting was set to 1280x720 since everything is so big.


Is it not possible for the MacBook to tell the display to use 1920x1080 instead of 3840x2160.



Reply
User profile for user: Grant Bennet-Alder
Grant Bennet-Alder
User level: Level 10
138,827 points

Sep 9, 2025 12:28 PM in response to net-engineer6

Two displays on one Thunderbolt-3 cable to the Dock:

The fundamental problem is that at 4K, each display takes about half the total 40 GHz bandwidth of a single Thunderbolt-3 cable to the Dock. So you are going to have trouble exceeding about 4K at 60 for each of TWO displays on the Dock.


Converting one to HDMI is a losing proposition because HDMI needs more bandwidth than half-a-ThunderBolt-3.


----

The HDMI port direct for M2 and later is a HDMI 2.1 port, which can support one display Directly at higher resolutions and bandwidths, for up to 42 GHz total. For 10 bits/color, up to 4K at 144Hz, or higher using Display Stream Compression.

The direct HDMI port and an ULTRA certified cable should be part of your solution.


-------

Unfortunately, the Caldigit Dock's DisplayPort output (or ThunderBolt-3 direct) is limited to DisplayPort 1.2, which is limited. That limitation is likely up to 4K at 75 Hz (possibly 95 Hz if you get lucky) and possibly slightly higher use Display Stream compression, all at 10 Bits/color.


For 8 bits/color, up to about 160 Hz using Display Stream Compression.



Reply

MacBook M4 Pro Dual Monitors Not Working

Welcome to Apple Support Community
A forum where Apple customers help each other with their products. Get started with your Apple Account.
Learn more Sign up