External Monitors Losing Connection Mac Pro

Question

Level 1

13 points

External Monitors Losing Connection Mac Pro

I've seen this issue discussed with people using MacBooks, but not with Mac Pro. And the solutions offered there don't work for me.

System Setup

2013 Mac Pro (trashcan) w/ 3 Apple thunderbolt displays (yes those older ones). The system has worked very well until now.

Problem

Sometime after Mojave update (about a month ago) one and sometimes two of the monitors just goes away. That means it won't come on and the Mac won't detect it. At first I only noticed it happening when the Mac would wake from sleep. Two monitors would come alive and the third would stay dark. But now it will happen when I'm working. The monitors will flicker and the most problematic one will display pixelated boxes in many colors. Sometimes the system will recover after 5 seconds; it will flicker the monitors and I'll be fine for a while longer. This will happen 2-4 times and eventually - usually 30 minutes to 3 hours - the flickering will happen and the monitor won't come back on. Then I'll be running with the other two. Sometimes when I come back to the machine the next day and wake it from sleep one of the other two monitors is off and then I'm down to one.

What I've Tried So Far

Unplugging the monitors from the thunderbolt connection and replugging it in doesn't work. Nothing happens. Same when I unplug and plug the monitor power back in. Also switching thunderbolt ports doesn't prevent the issue nor does it make the Mac see the other monitor. A reboot always fixes the issue temporarily.

Tried reset PRAM and SMC - no change.

What I cannot figure out is if this is a problem with the monitor, the Mac Pro itself, or some driver issue in Mojave. I poked around in the console but I am not familiar with it and couldn't find anything.

Any suggestion on where to look in the console or otherwise poke around to at least narrow down the issue would be most appreciated.

Thanks in advance

Mac Pro

Posted on Dec 28, 2018 3:49 PM

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Answer 1

acyclone Author

Level 1

13 points

Dec 29, 2018 6:23 AM in response to Grant Bennet-Alder

Some updates

Attached are the reports when all three monitors are working (after reboot). You'll see the dual graphics cards and all three displays.
Looks like the Apple Thunderbolt displays have the latest firmware. See this post
I will try changing it to have one display per BUS based on Apple's recommendation here (though it never mattered in the past).

Will post again once the third monitor gives out as before.

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Answer 2

acyclone Author

Level 1

13 points

Jan 6, 2019 6:45 AM in response to Grant Bennet-Alder

I am pretty sure there are not any separate sleep settings.

These are the Apple Thunderbolt displays and I've never seen separate settings for them.
I never changed any settings and they worked fine until Mojave.

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Answer 3

acyclone Author

Level 1

13 points

Dec 29, 2018 2:45 PM in response to acyclone

Two of my monitors "disappeared" after waking from several hours of sleep. See below for the results of the System Report. Shows the graphics cards are still there but the displays are not detected on the Thunderbolt busses. I have not changed where the monitors were plugged in so you will see that in this case bus 2 "lost" both monitors.

Ideas?

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Answer 4

Dec 28, 2018 5:57 PM in response to acyclone

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, no data will be sent to the display.

This query is only sent at certain times:

• at startup

• at wake from sleep

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• on invoking Option-(Detect Display) button in Displays preferences

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

Modern Displays with multiple ports are sometimes busy scanning the other ports, looking for an input, and miss the query from the Mac. They need to pay attention to the port you are actually using, or they will miss the query.

Some displays have On-Screen Display settings that can be used to tell the display a computer is attached on a certain port, or a certain port should be highest priority. Changing those may make your display more responsive.

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Answer 5

acyclone Author

Level 1

13 points

Dec 28, 2018 6:06 PM in response to Grant Bennet-Alder

Thanks for the reply.

if you read my post you will see that unplugging it and replugging doesn’t work. Option-Detect does not work either.

I also specified the type of display. I cannot find any settings that I can change for the apple thunderbolt displays.

Other thoughts?

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Answer 6

Dec 28, 2018 7:28 PM in response to acyclone

that still leaves sleep and wake that you did not dismiss.

About this Mac > (system Report) > graphics & displays ...

... can tell you what displays have actually been recognized, and which are truly among the missing. If a display is recognized, and does not show a picture, it is a different issue from not recognized at all.

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Answer 7

acyclone Author

Level 1

13 points

Jan 6, 2019 5:12 AM in response to acyclone

No love from the community? Issue still happens, but it is strange. I left for 5 days and computer was asleep. I had left all 3 monitors on with *mirrored displays*. When I came back all three monitors were working. As soon as I turned off mirrored displays the issue returned when I wake the computer from several hours sleep. I'm now on 3 separate thunderbolt buses.

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Answer 8

acyclone Author

Level 1

13 points

Jan 9, 2019 3:37 PM in response to acyclone

Either there is hardware going bad or there is an issue with the software and Thunderbolt. Now I have external hard drives connected via thunderbolt that are randomly being ejected (disconnected) during sleep. Wish I knew where to look in console to see what might be the issue....

Ideas?

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Answer 9

JLJ225

Level 1

13 points

Jan 12, 2019 10:56 AM in response to acyclone

I have seen similar issues since the Mojave update, but I am not using Apple monitors. I have one 4K Dell 27" and one non-4K HP Envy 32. I've noticed that they do not come out of sleep often when the Mac Pro has turned them off as part of power settings. Ideally, I'd like my Mac Pro to turn off the monitors after 15 minutes of inactivity and then sleep itself after an hour of inactivity, then when I move the mouse in the morning or after a break, everything wakes back up. What I'm finding that's similar to your issue is that sometimes only one monitor will respond, or it might be seemingly frozen on a black screen, but with still a little bit of light so you know the monitor is technically on. I also find when it comes out of sleep that each monitor will flicker on, then say it's going to sleep, then flicker back on. It's completely random. I also see where it will not remember my desktop image, which isn't a huge deal, just weird that it shows up in settings as having a custom desktop image, but won't necessarily display it with consistency. Since Mojave I've also found my Thunderbolt backup drive will not connect with regularity or will randomly disconnect. So much so that Time Machine stopped backing up and I had to use the USB port for the back-up drive.

Today, based on the comments in the thread, I went through the display menus to make sure they weren't sleeping on their own energy savings and the HP monitor appears to have it turned on, so I turned it off. I also changed the Dell 4K to a different bus to see if that helps.

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Answer 10

acyclone Author

Level 1

13 points

Jan 12, 2019 11:00 AM in response to JLJ225

Since someone else is having this issue I think it's more likely software than hardware. No changes on my issue. It sounds like you're having the same issue where thunderbolt is randomly going out and it's affecting the displays. Wish someone could tell us where to look in the console to try to diagnose the issue further.

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Answer 11

JLJ225

Level 1

13 points

Jan 17, 2019 8:17 AM in response to acyclone

As a test, I did a fresh install of Mojave 10.14.2 and did not reinstall anything from Time Machine just in case some little thing in my past system was causing the problem. The same thing has been happening with the fresh install. If I leave the system and it goes to sleep, waking it back up will cause the monitors to show a slightly lit black screen, but either nothing ever appears, or sometimes several minutes go by, some flickers of the monitors and the OS will appear at the login screen. I've also had completely random disconnects of both USB and Thunderbolt external drives... but that's a whole other problem.

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Answer 12

Jan 28, 2019 2:54 PM in response to acyclone

<<"No love from the community? ">>

Users answer with information they have when they have something to contribute. You got no answers not because of lack of LOVE, but due to failure to identify. No one else has your problem, or they would have chimed in with "Me, too!"

Your problem is unique and bizarre.

If you think you can reproduce the problem, you should make an appointment at the genius Bar and plan to bring as much of your equipment as possible.

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Answer 13

pcavaco

Level 1

4 points

Jan 30, 2019 7:39 AM in response to Grant Bennet-Alder

I've been having the same issue on a MacBook Pro (Retina, 15-inch, Mid 2015) since the upgrade to Mojave.

I have tried all of the troubleshooting steps mentioned in this thread and the issue persists.

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Answer 14

Jan 30, 2019 7:49 AM in response to pcavaco

On more recent Macs, deep sleep may drop the casual 5 Volt power to some USB and ThunderBolt devices, as the Mac tries to meet more end more stringent Energy Star requirements.

If a display adapter that uses that power (such as an off-Brand "legacy" adapter) is slow to wake up and stabilize, the display will miss the query from the Mac about its name and capabilities, will not respond, and will stay undiscovered and dark.

Try some of the discovery methods I listed above to see if the display wakes up and can be discovered.

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Answer 15

acyclone Author

Level 1

13 points

Jan 30, 2019 11:36 AM in response to Grant Bennet-Alder

Have already tried all the discovery methods listed. They don't work. I'm using Apple displays, which I'm guessing you don't consider to be "off brand"... Need someone who can help us sift through the console messages IMO.

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