iMac 2020 restarting randomly after connecting 2nd monitor

Question

iMac 2020 restarting randomly after connecting 2nd monitor

Same question as posted on April 12, 2021 from P_Craft: https://discussions.apple.com/thread/252655925

Two new iMacs in the office (Retina 5K, 27-inch, 2020; running Big Sur 11.3.1) that are connected to Dell P2719H second monitors. Every time they connect to the monitors, the computers shut down within an hour. The iMac goes black, the second monitor goes green and the computer reboots (takes a few minutes to restart - comes up with "computer restarted because of a problem" message).

They are both connected through HDMI - USB-C cables. We've tried different power sources (thought it was a power surge) but that didn't help. We're trying different cables currently.

Anyone have the same problem and any updates?!

iMac 27″, macOS 11.6

Posted on Nov 18, 2021 10:02 AM

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Answer 1

Best reply

rkaufmann87

Level 10

140,994 points

Nov 18, 2021 10:39 AM in response to alexgoesabroad

First thing to try is to restart in Safe Mode per Safe Mode Reset. If the reset does not help, the situation is likely due to the adapter being used to connect the Mac and/or the external display. Please check the external display website to see if they have any firmware updates for it and also please do the same for the adapter you are using. If you still have no luck, please use other adapters.

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Answer 2

rkaufmann87

Level 10

140,994 points

Nov 19, 2021 9:51 PM in response to alexgoesabroad

It will help us get a good idea of what is causing your problem if you provide a report of your system, that way we do not have to play 20 questions with you. The report we are requesting does NOT provide any personal information and is extremely safe to use. Please navigate to www.Etrecheck.com and download the free version of EtreCheck. Once you have you downloaded the app and installed it, please run the report and save it. This report will help us get a good idea what has been installed on your system and help us be able to diagnose what may be wrong.

When you have your report, you can attach it when you reply to this message and we can then review it and help you determine what is needed to get your system running well again.

For instructions on how to download your EtreCheck report and attach it to your reply to this message please click https://discussions.apple.com/docs/DOC-250000211

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Answer 3

Nov 19, 2021 11:28 AM in response to den.thed

Using the USB-C to DisplayPort cables did not fix the problem. The computer shut down almost immediately. We've tried other HDMI cables with adapters, same issue. I even brought in my own Asus second monitor but the computers still shut down using that.

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Answer 4

Nov 19, 2021 5:44 PM in response to den.thed

We’ve already worked with AppleCare and have tested new computers with the same issue. Two brand new computer doing the same exact thing?! It’s completely beyond comprehension and we’re at our wits ends trying to understand why a second monitor is all of a sudden incompatible with new computers

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Answer 5

rkaufmann87

Level 10

140,994 points

Nov 19, 2021 11:33 AM in response to alexgoesabroad

Might be time to contact AppleCare. If you are in the USA please call 800-275-2273. Outside the US please AppleCare contact Information to get the phone number for your area.

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