MacBook Air (M1, 2020) does not recognise external monitor connected directly to USB-C port when a dongle with an HDMI port is connected to the other USB-C port

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Level 1

9 points

MacBook Air (M1, 2020) does not recognise external monitor connected directly to USB-C port when a dongle with an HDMI port is connected to the other USB-C port

Is anyone else having this problem, or does anyone have a solution?

My guess is that this has to do with the M1's being limited to one external display, and somehow it recognises the (unused) HDMI port on the dongle and ignores the external display connected directly to the other USB-C port.

Steps to replicate:

Connect USB-C dongle with an HDMI port (not in use) to MacBook. I have tested with two dongles from different makers, Satechi and VAVA.
Connect external display (Dell P2415Q) to MacBook directly with USB-C to DisplayPort cable.
MacBook does not recognise external display.

Similarly:

Connect external display (Dell P2415Q) to MacBook directly with USB-C to DisplayPort cable. Since this is done first, the MacBook recognises the display without issue.
Connect USB-C dongle with an HDMI port (not in use) to MacBook. MacBook maintains its connection to the external display. However:
Put MacBook to sleep.
Wake MacBook. External display is no longer recognised.

Thanks for any discussion/help.

MacBook Air

Posted on Nov 26, 2020 5:28 PM

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Answer 1

Nov 27, 2020 3:50 AM in response to aleyon

If what I understand you are trying to do correctly, the new

M1 MacBook Air only supports a single external display, so

you cannot use two displays.

Also, FWIW, HDMI interface has had various issues across all Macs.

The only truly reliable was some adaption to DisplayPort or DVI-D.

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Answer 2

aleyon Author

Level 1

9 points

Nov 27, 2020 2:51 PM in response to woodmeister50

Thanks for your reply.

The HDMI port is NOT in use. I am only trying to connect ONE monitor via a USB-C to DP cable.

My theory is that the simple existence of a hdmi port on the dongle confuses the MacBook and causes it to fail to recognise the external display when connected.

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Answer 3

Steve RK

Level 1

11 points

Dec 2, 2020 8:41 AM in response to aleyon

I think you are right. I am having the same experience with my M1 MBA. It's quite annoying. I could not get it to recognize my external 4K monitor via the USB-C port on the computer. When I unplugged the dongle, it recognized it. Like you, the HDMI port on the dongle is not in use. I can re-plug the dongle once the monitor is recognized, and it still works. This is some kind of a bug.

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Answer 4

aleyon Author

Level 1

9 points

Dec 9, 2020 7:52 PM in response to aleyon

My workaround in the meantime (involved buying another dongle):

I bought the Cable Matters USB-C Multiport Adapter with 8K DisplayPort, 2x USB 2.0, Fast Ethernet, and Power Delivery which allows me to have display out and power in via one USB-C port.

I use the other USB-C port for a powered USB 3.0 hub (to connect external storage, wireless mouse dongle, card reader, etc.).

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