USB-C Displayport doesn't work until HDMI is plugged in too

Question

USB-C Displayport doesn't work until HDMI is plugged in too

I'm trying to connect an external monitor (AOC Q27P2CA) to my 2021 Macbook Pro 14" M1 running Monterey using a USB-C cable, but the monitor isn't detected. The weird part is that if I also connect using an HDMI cable, the Macbook then detects the monitor twice. I can then unplug the HDMI cable, and the USB-C connection works perfectly, including charging the Macbook. Until the Mac goes to sleep, at which point it loses the monitor, and when I wake it up, I have to plug in the HDMI cable again to trigger detection of the USB-C connection, then unplug the HDMI cable again.

It seems as though the Macbook needs to have a monitor connected via HDMI before it can detect a monitor connected via USB-C. I could just use HDMI, but I would ideally like to use the monitor's USB hub and charge the Macbook all just with a single cable connecting them.

Posted on Apr 5, 2022 8:38 AM

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Answer 1

Top-ranking reply

User7584-5043 Author

Level 1

5 points

Apr 13, 2022 7:56 AM in response to melissa_m77

AOC have pointed me to an obscure setting in the monitor's OSD which keeps USB powered on when the monitor is in standby, and that has resolved the problem of the monitor getting "lost" when the Macbook sleeps. The original issue about the initial detection of the monitor is unresolved, but as that's only really a first-time setup annoyance, I can live with that.

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Answer 2

bailier

Community Specialist

Apr 6, 2022 11:03 AM in response to User7584-5043

Hello User7584-5043,

We suggest trying the steps here: If your external display isn't detected or appears blurry when connected to your Mac - Apple Support

If that doesn't help, try using a different cable to see if the issue persists.

If the above doesn't help, try rebooting into safe mode to see if the issue is present: How to use safe mode on your Mac - Apple Support

Let us know the results.

Best Regards.

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Answer 3

Trish313

Community Specialist

Apr 8, 2022 6:31 AM in response to User7584-5043

User7584-5043,

From the Mac side of things, you can confirm that your Mac is running the latest version of macOS Monterey available which is currently macOS 12.3.1. You can do this by going to Apple Menu (  ) > System Preferences > Software Updates.

Update macOS on Mac

Take care!

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Answer 4

Apr 8, 2022 1:08 AM in response to bailier

Thanks for the suggestions. I've tried all of those, and still have the same issue, even in safe mode.

I have also now discovered that while the monitor is connected only by the USB-C cable, I can trigger detection of the monitor by turning the monitor off and back on. After doing that, everything works fine.

As this is clearly an issue with communication between the Macbook and the monitor, I have also raised a support ticket with AOC, the monitor manufacturer, to see if there's anything they can suggest. But is there anything else I can try on the Mac side of things?

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Answer 5

Apr 9, 2022 6:16 AM in response to User7584-5043

Hello User7584-5043,

Thank you for taking that step.

If updating didn't resolve the issue, and you've had a chance to try a different cable, you'll want to reach out to Apple Support for further assistance: Get Support.

Take care.

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Answer 6

Apr 9, 2022 3:18 AM in response to Trish313

Thanks - that was a good suggestion - I was a little out of date, but unfortunately it hasn't made any difference. I'm now on 12.3.1 and still have the same issue.

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Answer 7

Sheree_P

Community Specialist

Apr 13, 2022 8:12 AM in response to User7584-5043

Hey,

Since you still experiencing the issue where you have to connect HDMI cable in order for it to come on, we recommend contacting Apple Support here: Get Support.

Take care.

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USB-C Displayport doesn't work until HDMI is plugged in too

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