Screen flashing after wake from sleep

Question

Level 1

15 points

Screen flashing after wake from sleep

Suddenly, after waking from sleep, the iMac retina display keeps flashing to black and back to the normal desktop screen repeatedly.

I've tried to fix it:

• Safe-boot. But that wouldn't complete the startup. Just hangs after the progress bar completes.

• Shut down from the power button and then startup. Still flashing.

• Clean My Mac and restart. Says Mac is in good shape now. Still flashing though.

• Upgrade from Catalina. (Tried it while the screen flashed continuously.) Hours waiting for MontereyOS to finish installing, but hangs every time at 12 minutes. Tried twice. Would never finish. Shut down from power button. Startup, still flashing.

The only thing that seems to work the past few days is to shutdown then startup holding down command-option-P-R. But couple times using this technique the first attempt didn't work and the screen flashed and the beachball spun erratically and displayed psychedelic colors.

Please help.

iMac 27″, macOS 10.15

Posted on Mar 16, 2022 3:03 AM

Reply

Answer 1

Top-ranking reply

MrKwe Author

Level 1

15 points

Mar 17, 2022 7:10 PM in response to Chris_C1

I found the problem and the flashing stopped.

I experimented with the Energy Saver settings and discovered that the Sleep function was not the cause.

Allowing the display to go off but not allowing sleep, and then “waking” the display caused the screen constant flashing.

So Sleep Mode was not the problem.

The iMac is connected to a TV via HDMI cable.

I had noticed that the Displays preference pane would sometimes not load (an error message appeared sometimes) and when the preference pane did load normally, the preference window for the TV display opened up also, without me clicking the button for it.

While the iMac was flashing, I disconnected the HDMI cable at the iMac port. The iMac screen flashing instantly stopped.

It turns out he HDMI cable was slightly loose in the port, and also the outer plastic casing is cracked and the inner wires are exposed near the plug. However the inner wires are not frayed.

I haven’t investigated further regarding the condition of the HDMI cable, or reinserting the cable securely, or replacing the cable, etc.

At the moment I’m just pleased to have my screen stop flashing.

Reply

Answer 2

Chris_C1

Community Specialist

Mar 17, 2022 7:09 AM in response to MrKwe

Hello MrKwe,

Welcome to Apple Support Communities!

Try some of the steps below and see if any of these correct the issue:

If the display is black or dim: Try adjusting your display’s brightness.

If images are too large or too small: Try adjusting your display’s resolution.

If the colors don’t look right: Try using the display profile designed for your display. For example, if you’re using a Thunderbolt display, choose Apple menu > System Preferences, click Displays , then select Thunderbolt Display in the Color Profile list. If that doesn’t work, try calibrating the display.

If your display is blurry: Make sure your Mac has detected that display. Choose Apple menu > System Preferences, then click Displays.

To see the Detect Displays button, press the Option key. Then click the button to detect the display.

If the display is flickering: Make sure your Mac and display are connected to one another with good quality cables and adapters. You may also be experiencing interference from a nearby power line, a fluorescent light, a radio, a microwave oven, another computer, or another electrical device. Try relocating nearby electrical devices, or moving your Mac and display.

If you see bright or dark spots on a flat-panel or Mac notebook computer screen: Your display may have pixel anomalies. If you suspect your Apple display contains a high number of anomalies, take it to an Apple Authorized Service Provider.

If none of these solutions work: If you have an Apple display and can’t correct the problem, contact an Apple Authorized Service Provider for more help. Don’t attempt to repair the display yourself, because any damage you may cause is not covered under your warranty.

If your Mac display doesn’t look right

Another good resource for this behavior is: If your Mac screen goes black

Let us know if you have any questions.

Thank you for using Apple Support Communities.

Take care!

Reply

Answer 3

AppleJen77

Community Specialist

Mar 18, 2022 6:07 AM in response to MrKwe

Excellent!

Glad you were able to resolve the issue. Feel free to reach out again if you need further assistance and have a great day!

Reply

Screen flashing after wake from sleep

Similar questions