Computer screen and external monitor randomly go black

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Level 1

4 points

Computer screen and external monitor randomly go black

Hi,

I have an iMac (3.8 GHz 8-Core Intel Core i7) running Sequoia 15.6, connected to an external MNN display via a Type-C cable (plugged into the "Full Function Type-C Port" on the monitor).

Randomly throughout the day, both screens will go black. The computer continues to run in the background for about a minute and then stops responding. The only way to get the screens back on is to do a force restart.

I had a similar issue a couple of years ago with the same iMac but a different external monitor. I was never able to resolve it, so I stopped using the external display altogether.

Any idea what could be causing this or possible solutions?

Thanks!

Joanne

iMac 27″, macOS 15.6

Posted on Aug 7, 2025 10:01 AM

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Answer 1

den.thed

Level 10

89,116 points

Aug 7, 2025 11:04 AM in response to jojoyahn

This sounds more like Automatic Computer is causing the iMac to crash and forcing a restart.

As a test

Turn On "Prevent automatic sleeping when display is off"

Set "Turn display off when inactive" to 5 or 10 minutes

Leave the iMac On and only allow the display(s) to turn Off

Do not manually Sleep from the Apple Drop Down menu

Shut Down the iMac when away for a day or more

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