Mac Mini (M1) dual display doesn't work.

Question

Mac Mini (M1) dual display doesn't work.

I'm enjoying my Mac mini with the M1 soc but unfortunately connecting two monitors does not work. Upon fresh boot, both monitors display correctly on login screen. However, when logging in, both monitors start flickering (see video). I have to disconnect and reconnect one hdmi cable for displays to work again. I currently have one one monitor connected through the HDMI port; the second monitor is connected with a USB-C to HDMI adapter. I should clarify that both monitors work perfectly on their own; the issues come when both are connected. Any ideas?

I've liked a video of flickering. The apps are non-responsive when flickering is occurring.

Mac mini 2018 or later

Posted on Nov 20, 2020 8:09 PM

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Answer 1

taro0922

Level 1

4 points

Nov 21, 2020 11:45 PM in response to whatisdeadmayneverdie

Exact same issue here with my new M1 Silicon Mac Mini. I uninstalled and reinstalled the latest OS ver 11.0.1 but didn't solve. I am uploading a video showing the issues:

https://drive.google.com/file/d/19DXVkPxUVI6wt4f-7Qx_fc_1_xfddXOZ/view?usp=sharing

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Answer 2

hcsitas

Level 6

10,038 points

Nov 22, 2020 12:00 AM in response to whatisdeadmayneverdie

How long are the cables?

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Answer 3

taro0922

Level 1

4 points

Nov 22, 2020 12:05 AM in response to hcsitas

The HDMI cables are both around 2 meters long. One of the HDMI cables is directly connected to the Mac Mini and the other one is connected through a USB C to HDMI adapter (belkin).

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Answer 4

Nov 22, 2020 12:51 AM in response to whatisdeadmayneverdie

I have the same issue on my M1 Mac Mini too. I'm connecting using an HDMI cable for one screen and USB-C to HDMI cable on the other. Both screens work perfectly fine until I log back in after a reboot, sleep or shutdown.

As soon as I log back in, both screens flicker. Sometimes the screens have swapped positions too, with the background image changing on one screen and the refresh rate changed from 144Hz to 60Hz. The menu bar is still visible and I can get to System Preferences so that I can 'reset' the screens by changing their properties back to how I had them setup originally.

If I use only one screen, there doesn't seem to be an issue either with the HDMI cable or USB-C to HDMI cable.

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Answer 5

hcsitas

Level 6

10,038 points

Nov 22, 2020 12:57 AM in response to taro0922

Anything more than 1m = problem.

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Answer 6

hcsitas

Level 6

10,038 points

Nov 22, 2020 12:58 AM in response to Highbury_

Check cable length and limit it to 1m.

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Answer 7

Nov 22, 2020 4:54 AM in response to whatisdeadmayneverdie

FWIW, if any of the displays have a Display Port input,

get a USB-C to DisplayPort adapter or USB-C to DisplayPort cable

and connect with a DisplayPort cable.

https://www.amazon.com/s?k=usb-c+to+displayport&crid=12E2A10YXV6AC&sprefix=USB-C+to+%2Caps%2C171&ref=nb_sb_ss_ts-a-p_6_9

Over the years there have been numerous issues with connecting MacMinis

to the non-HDMI ports with any HDMI adapter. One would thing that may

have been solved by now, but perhaps not.

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Answer 8

Nov 22, 2020 8:47 AM in response to woodmeister50

Thanks for the suggestion. I will try this. Might be a couple of days since I first have to order it and wait for adapter to arrive. Both my monitors have a Display Port port so will give it a try. At first I thought I had a defective Mini but given others are having same issue then it’s probably a support problem. We’ll see.

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Answer 9

Nov 22, 2020 8:50 AM in response to taro0922

That’s exactly what happens to me. Mmm...someone below suggested trying a USB-C to Display Port instead of HDMI so I may be able to try that next. Let me know if you find a solution. Pretty disappointing this happens on the new Mac Minis. Other than this issue the Mac is working great.

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Answer 10

Nov 22, 2020 10:38 AM in response to whatisdeadmayneverdie

I have exactly the same issue (and I think the same monitors) as you. It worked great for the first couple of hours but now, not so great.

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Answer 11

Nov 22, 2020 10:40 AM in response to BillyBrown301

It works for me until I put the Mac on sleep or reboot. Are you also using an USB-C to HDMI adapter?

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Answer 12

Nov 22, 2020 10:48 AM in response to whatisdeadmayneverdie

I can’t get it to work at all now ... just get exactly the same flicker as you do.

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Answer 13

Nov 22, 2020 10:58 AM in response to BillyBrown301

Usually when I get the flicker I have to do the following:

I disconnect the USB-C adapter and only connect one monitor through the HDMI port. (No USB-C should be connected to any of the ports).
I reboot and login to the system (only one monitor connected)
Once logged in, everything should be working fine with one monitor
I connect the second monitor by plugging the USB-C connector.
The second monitor should display fine and both should work until next time you reboot or put Mac to sleep.

*if this doesn't work, then I do the exact sequence but starting with the USB-C instead of the HDMI.

***** this is happening to us. I'm still not sure if it is a Mac issue or adapter issue.

Earlier today I noticed this on the Mac mini specs page:

Simultaneously supports up to two displays:

One display with up to 6K resolution at 60Hz connected via Thunderbolt and one display with up to 4K resolution at 60Hz connected via HDMI 2.0

Thunderbolt 3 digital video output supports

Native DisplayPort output over USB‑C

Thunderbolt 2, DVI, and VGA output supported using adapters (sold separately)

HDMI 2.0 display video output

Support for one display with up to 4K resolution at 60Hz

DVI output using HDMI to DVI Adapter (sold separately)

https://www.apple.com/mac-mini/specs/

So maybe Mac mini doesn't support connecting two displays via HDMI, maybe one has to be Display Port as the specs do list it as supporting 'Native DisplayPort output over USB‑C".

I'll ponder about buying a USB-C to Display Port adapter to try.

For now I'm just using one monitor since I don't want to be disconnecting/connecting cables each day...

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Answer 14

Nov 22, 2020 11:01 AM in response to whatisdeadmayneverdie

I have the same issue, but want to add that this also occurs when exiting sidecar.

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Answer 15

Nov 22, 2020 11:02 AM in response to whatisdeadmayneverdie

Yes - that mirrors exactly my issues too and ways to resolve them. A bit frustrating - especially how good the rest of the machine is! My monitor only has HDMI and so I’m not 100% sure of next steps...

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