Multiple 4K Display @30hz in certain rotation (90 degrees)

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Danielee715 Author

Level 1

18 points

Multiple 4K Display @30hz in certain rotation (90 degrees)

I am using two external displays via USB-C on my mac (Big Sur 11.0.1)

Main Monitor 4K : LG 27UK600 (Standard)

Sub Monitor 4K : LG 27UL850 (Vertical Setup)

They are both connected via USB-C

When they are at all standard mode they are both fine at 60hz rate.

However whenever I change my second display to a 90 rotation setup, the refresh rate from my other display drops to 30hz.

The real funny thing is that if I change it to 270 degrees, it is all back at 60hz.

Unfortunately my display can only rotate 90 degrees.

So to sum up, when I rotate my second display 90 degrees(and only 90), the first display's refresh rate drops to 30hz.

What is the problem? I cannot come to a logical explanation to this problem.

FYI. For some reason the HDMI connection from my mac to the display does not work after I updated to Big Sur... so I am using a HDMI to USB C cable(60hz compatible) for one and USBC to USBC cable for the other. Hoping that this will be fixed by apple in future update.

Please Help!

Thank you.

Mac mini, macOS 11.0

Posted on Nov 22, 2020 11:24 PM

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Answer 1

den.thed

Level 10

91,516 points

Nov 23, 2020 4:55 AM in response to Danielee715

Do you have one display plugged into Bus 0 and the other plugged into on Bus 1.......?

Have you tried reversing the cables and then re-arranging the display setup....?

Perhaps you just need to reset the Mac Mini's NVRAM.....

https://support.apple.com/en-us/HT204063

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Answer 2

Danielee715 Author

Level 1

18 points

Nov 23, 2020 5:17 PM in response to den.thed

Thank you for your reply...

Do you have one display plugged into Bus 0 and the other plugged into on Bus 1...

Yes. One on the 1st slot, and one on the 3rd.

Have you tried reversing the cables and then re-arranging the display setup....?

Just did. Still the same.

Perhaps you just need to reset the Mac Mini's NVRAM.....

Did that also several times already. Not working.

This is driving me crazy... any other ideas?

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Answer 3

den.thed

Level 10

91,516 points

Nov 24, 2020 12:08 PM in response to Danielee715

Danielee715 wrote:

Thank you for your reply...

You're welcome.

This is driving me crazy...

To be honest, I'm not sure why 90 degrees and 270 degrees would report different Hz.

any other ideas?

Anyway you can move and live with the vertical display on the right side of the main display and go 270 degrees.

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Answer 4

Danielee715 Author

Level 1

18 points

Nov 24, 2020 5:52 PM in response to den.thed

Thanks for the reply.

Anyway you can move and live with the vertical display on the right side of the main display and go 270 degrees.

I wish I could do that... but my monitor stand only rotates to 90 degrees, and does not turn the other way around(270).

Meanwhile, yesterday I had an Idea. This was the setting I had before.

Display A : USB C to USB C connection. "The one that I want to rotate 90 degrees."

Display B : HDMI to USB C (Dongle) connection. "The one that turns 30hz once Display A turns 90 degrees."

Now I changed Display A from a USB c to USB C to a HDMI to USB C (Dongle) setting... just to see how it reacts.

Display A : HDMI to USB C (Dongle) connection.

Display B : HDMI to USB C (Dongle) connection.

And how both are working fine at 60hz even thought I have the Display A at 90 degrees.

It is a work around for me for now.... but I am working with two dongles on the back of my Mac Mini, which is frustrating

What do you think is the problem? The display(LG)? The OS(Big Sur)? I am curious on why this happens.

One other thing. My HDMI port does not work also after I upgraded to Big Sur. So now I have an empty HDMI port on my Mac Mini with two USB C on each Bus connected with dongles... not ideal.

Thanks.

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Answer 5

den.thed

Level 10

91,516 points

Nov 24, 2020 6:47 PM in response to Danielee715

Danielee715 wrote:

It is a work around for me for now.... but I am working with two dongles on the back of my Mac Mini, which is frustrating

Nothing wrong with that, if it gets you where you want to be.

What do you think is the problem? The display(LG)? The OS(Big Sur)? I am curious on why this happens.

If the setup was working before BS, then it's BS. Plus with all the other folk complaining about display issues, I suspect that the macOS development team is working on a solution and update as we speak.

One other thing. My HDMI port does not work also after I upgraded to Big Sur. So now I have an empty HDMI port on my Mac Mini with two USB C on each Bus connected with dongles... not ideal.

If the HDMI port was working before BS, then again it's BS. Not wrong with that, the 2018 Mac Mini is perfectly capable of running 2 displays on the USB-C ports. If you need more USB-C ports, you can always use a USB-C hub in-between the where the displays are connected.

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Multiple 4K Display @30hz in certain rotation (90 degrees)

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