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

USB Hub recognized as external display, but connecting a display to the hub does not work

I have a 16" MacBook Pro 2021 with an Apple M1 Pro chip running macOS Monterey v.12.2.1 (see screenshot 1 for more details). I also have a 27" Dell external monitor (model P2722HE) connected using a USB-C cable directly to the laptop. I am also using an 11-in-1 USB-C Hub+ (not really sure of the brand, the package just says "Made in China") to connect my keyboard, webcam, and headset (all USB-A 2/3 connections).


My issue is that within System Preferences > Displays (see screenshot 2) or About This Mac > Displays (see screenshot 3), there are two external displays being shows, one which is 27" (the real Dell monitor) and the other which is 31.5" (not a monitor that I have in reality). After some playing around with things, it appears that the 31.5" display is showing up when the USB-C hub is connected to the laptop. However, when I switch the Dell monitor from being connected directly to the laptop to instead using the USB-C hub, the display does not recognize the connection.


From some Googling, this appears to be a sporadic issue for other users with a MBP using the M1 chip running macOS Monterey. Is this a bug that can be fixed?


Screenshot 1


Screenshot 2

Screenshot 3




[Image Edited by Moderator to Remove Serial Number]


MacBook Pro (2020 and later)

Posted on Feb 24, 2022 1:35 PM

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User profile for user: BobHarris
BobHarris
User level: Level 9
55,055 points

Posted on Feb 24, 2022 5:17 PM

A USB-C hub can support a single DisplayPort signal from the Mac, when the hub can keep as DisplayPort, or convert to HDMI, DVI, VGA.


Any USB-C ports on your USB-C hub will just be USB 3 ports. These USB ports may support 5 or 10 gigabits/sec USB, but those hub USB ports will not also propagate the single DisplayPort it got from the Mac. A USB-C hub gets just 1 DisplayPort and the hub would have split that off to a specific video port.


If this were a Thunderbolt dock, then it would be able to support multiple displays, and if it then had a Thunderbolt out port, that would allow you to plug in your DELL monitor.


I have a CalDigit Thunderbolt 3 dock, and I can plug in my DELL Q3219U 32" 4K monitor's USB-C cable into my Mac, or the CalDigit Thunderbolt 3 output port. But I cannot plug my DELL into one of the CalDigit USB-C output ports, because they are just USB 3.1 gen 2 ports.

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User profile for user: BobHarris
BobHarris
User level: Level 9
55,055 points

Feb 24, 2022 5:17 PM in response to mgz_peloton

A USB-C hub can support a single DisplayPort signal from the Mac, when the hub can keep as DisplayPort, or convert to HDMI, DVI, VGA.


Any USB-C ports on your USB-C hub will just be USB 3 ports. These USB ports may support 5 or 10 gigabits/sec USB, but those hub USB ports will not also propagate the single DisplayPort it got from the Mac. A USB-C hub gets just 1 DisplayPort and the hub would have split that off to a specific video port.


If this were a Thunderbolt dock, then it would be able to support multiple displays, and if it then had a Thunderbolt out port, that would allow you to plug in your DELL monitor.


I have a CalDigit Thunderbolt 3 dock, and I can plug in my DELL Q3219U 32" 4K monitor's USB-C cable into my Mac, or the CalDigit Thunderbolt 3 output port. But I cannot plug my DELL into one of the CalDigit USB-C output ports, because they are just USB 3.1 gen 2 ports.

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User profile for user: lllaass
lllaass
User level: Level 10
210,459 points

Feb 24, 2022 2:40 PM in response to mgz_peloton

Does the hub have an HDMI port or other video-only port?

If it does then it sounds like the Mac is seeing that video port as a display.


You also said "However, when I switch the Dell monitor from being connected directly to the laptop to instead using the USB-C hub, the display does not recognize the connection.."

For some hubs not all ports work with Monterey. It seems to be dependent on the chips in the hub. Since many hubs are just rebranded ons it is hard to tell what is inside just base on the label on the hub.

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USB Hub recognized as external display, but connecting a display to the hub does not work

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