Using Macbook Pro with an external monitor

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Level 1

8 points

Using Macbook Pro with an external monitor

I have a 2020 M1 Max Macbook Pro 16 inch which I just bought. Connecting it to a 49" AOC ultrawide monitor. So far it's been an amazing experience. I connect via a USBC / DP adapter to get the 165 hz.

I also have a MSI Windows Laptop, which I connect via the USB-C

I have 2 laptops lids closed. And so far the Mac works ok with the lid closed.

Problem happens when I switch display from DP (Mac) to USBC (Windows). When I switch back, it's no longer available. It's as if the Macbook went to sleep. In order to get it back, I need to open up the Macbook lid, log in, wait for 1-2 minutes, then close it back again and it works fine again.

This is annoying especially if I need switch between screens, and each time I go back to Mac I need to open the lid and close again in order to revive the external display. Windows laptop works fine.

Tried Amphetamine, and all the usual stuff recommended in the energy settings. How do I fix this?

MacBook Pro 13″, OS X 10.11

Posted on Sep 19, 2023 5:23 PM

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Answer 1

Top-ranking reply

Grant Bennet-Alder

Level 10

140,309 points

Sep 19, 2023 5:50 PM in response to hexies

The Mac uses a system that reminds me of “Plug and play” to determine what display is connected, and what its capabilities are.

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)

so try doing some of those things and see if the display comes alive.

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Answer 2

Sep 19, 2023 6:41 PM in response to hexies

Um, no.

The Mac is actively monitoring any transmission error that occur on the link, and it detects when the display is not present [reality]. You are asking it to pretend the display is still there.

The Mac does not work that way.

When a display is detected, the Mac sets its resolution based on the display's stated capabilities. Connect a different display, and the Mac changes the resolution. connect NO display and it stops the fastest, least forgiving steady data transfer in the computer from wasting resources for nothing.

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Answer 3

hexies Author

Level 1

8 points

Sep 19, 2023 6:30 PM in response to Grant Bennet-Alder

Thanks Grant for the in-depth reply, very helpful to understand the issue at hand.

Everything suggested seems to require manual intervention by the user, like opening the lid, replugging the wire etc. Is there some setting that doesn’t require this?

My windows laptop works fine switching the display away and back again. Anything I can do to mimic that?

Feels like my MBP should be intuitive enough to keep the DISPLAY on all the time

Thanks!

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Answer 4

hexies Author

Level 1

8 points

Sep 19, 2023 7:18 PM in response to Grant Bennet-Alder

Understood now.

wow this got “resolved” faster than I thought . I expected a proper answer to take forever here.

Youre amazing, thanks for your help.

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Using Macbook Pro with an external monitor

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