Extra Display to iMac Pro Unreliable Connection with USB-C

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Level 1

14 points

Extra Display to iMac Pro Unreliable Connection with USB-C

Initially tried to connect an old Asus screen to my iMac Pro using an HDMI cable and an HDMI to USB-C connector. This gave an intermittent connection - sometimes it was there, and when I got it to appear then it stayed all day, but often when starting up after shut down the Asus display would say it wasn't getting a signal. When this happened the iMac Pro did recognise the presence of the Asus display since I normally have the dock in the secondary display and the dock disappeared when I turned the power on the Asus display.

Bought a new, more expensive HDMI connector and found the same problem. So I decided to buy a new LG display with a USB-C connection. Now that is showing the same problem. Occasionally the LG display says it has no signal, but the iMac thinks it is there. Fiddling with the leads usually sorts this problem but it is a right pain to have to do it every morning and sometimes it takes a lot of fiddling.

I have read a few threads about dodgy connections and convertors between iMac Pros and displays but I am surprised it is happening with USB-C. Is anyone else getting this?

iMac Pro (2017), macOS High Sierra (10.13.2), 2TB Flash Drive

Posted on Jan 31, 2018 1:20 AM

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Answer 1

DonH49

Level 6

16,704 points

Jan 31, 2018 4:23 PM in response to Alan James

I don't know how important it is to you to not mess with setups. If it bothers you and you don't want problems then buy a real good condition Apple27 inch Thunderbolt Display and use the Apple TB3 to TB3 dongle and your problems are over. Sell the Asus.

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Answer 2

Alan James Author

Level 1

14 points

Feb 1, 2018 1:13 AM in response to DonH49

I must have not explained it very well.

I have sold the Asus and bought a new LG display with USB-C connector, basically the latest model and an excellent display (better than the ancient Apple 27" monitor). It is with this new LG monitor, connected by the USB-C lead with no convertors, that I am getting the problem.

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Answer 3

Yzord

Level 1

17 points

Feb 1, 2018 1:30 AM in response to Alan James

I am having the same issue here. Bought 2x LG 27UD88 4K displays with USB-C and connected them each to one USB-C controller since the Pro has two of them. In the morning when i wake up the iMac Pro, it cannot detect one of the screens. Even today, it detected both the LG screens, but not its own screen. And yesterday it detected its own screen and one LG screen and the other stayed black and telling me there was no signal.

Yesterday i could fix it by taking out the USB-C cable out of the LG screen and push it back in. But today i didn't had such option with the iMac screen so i had to reboot which i lost my work i was working on.

And apparently more people have this issue 😟

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Answer 4

Alan James Author

Level 1

14 points

Feb 1, 2018 1:34 AM in response to Yzord

Yes, that is exactly what I am experiencing and I have the same LG display, however I was also getting the problem with the Asus display connected via HDMI and convertor as mentioned. I have never had it not detect its own display yet.

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Answer 5

Yzord

Level 1

17 points

Feb 1, 2018 1:44 AM in response to Alan James

So it is not the LG who is doing weird. Because today the screen of the Pro had no signal, but the Pro was running. I had signal on both LG's and could restart the Pro the normal way.

So, it looks like we have a hardware issue here.

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Answer 6

Feb 3, 2018 11:56 AM in response to Alan James

It seems the USB-C port physical tolerance might be a bit tighter on the iMac Pro.
I tried reversing the USB-C side of the cable (which really shouldn't make a difference with USB-C) and I was able to get a solid "snap" at which point the monitor was recognized.

See if you can get the USB-C side of the cable to give you a solid snap. It may clear up the intermittency.

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Answer 7

Feb 1, 2018 2:50 PM in response to Alan James

And I'm trying USB-C to HDMI and can't get it working with two different monitors. Extra Display to iMac Pro Unreliable Connection with USB-C

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Extra Display to iMac Pro Unreliable Connection with USB-C

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