iMac screen flashing

Question

Level 1

8 points

iMac screen flashing

Hello

My screen suddenly started flashing and then eventually goes black. Power button might bring it back or often needs restart. After restart it begins again after a few minutes

I have tried:

- power down and unplug

- disk verify / repair - no issues found

- restart+option+command+p+r

- uninstalled Firefox, as mentioned online as possible cause

- ran diagnostic hardware test, restart+D, no trouble found

- ran diagnostic extended hardware test, no trouble found. ***screen did not flash for all 1.5 hours while in diagnostic mode ***

- safe restart - also flashed, but probably took longer for it to begin

Specs are as follows:

10.9.5

iMac13,1

Quad core Intel core i5

Cpu speed 2.7 GHz

Number of cores 4

L2 cache per core 256KB

L3 cpu cache per cpu 6MB

SMC version 2.9f5

Graphics Nvidia GeForce GT 640M

VRAM 512 MB

Memory 16GB (8GB×2) 1600Mhz

Storage 300 GB used of 999GB

iMac Pro

Posted on Jul 14, 2020 1:28 PM

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Answer 1

Jul 16, 2020 2:13 AM in response to GeMu00

GeMu00 wrote:

Update: Unfortunately the flashing started again, same as before reinstalling OS. The Guest account is now also flashing (it had started before doing the OS install). It took 2 hours to run the Disk Utility and Install in recovery mode, during which there was no flashing. Also there is no flashing in the Login screen.

So as I understand it, flashing continues to appear in your main and guest account despite reinstalling macOS. This would seem likely to be a hardware fault. Sorry about that.

I think your only option left, before using it as a paper weight, is to boot into Internet Recovery mode - Option (⌥) - Command (⌘) – R on startup (this ensures you get a fully uncorrupted version of macOS - erase your internal drive, reinstall macOS but don't restore anything from backups at this point.

Then test, test, test.

If it still fails - with none of your personal data on it - it's a hardware fault.

If it works, it's a data issue and you probably want to manually reinstall your apps and personal data.

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Answer 2

Jul 14, 2020 1:50 PM in response to GeMu00

Are you able to log into the guest account?

If so, does the problem disappear when in the guest account?

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Answer 3

Jul 15, 2020 7:16 AM in response to GeMu00

OK. If the guest account works perfectly then you probably need to tidy up your user account.

Reboot into recovery mode (Command-R on startup)
Then run First Aid on the internal drive via Disk Utility.
Then quit Disk Utility and then reinstall macOS

See if that helps.

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Answer 4

GeMu00 Author

Level 1

8 points

Jul 16, 2020 10:39 AM in response to The_Knowledge_Seeker

Thanks for all your help with this. At this stage I'm going to bit the bullet and get a new machine. I do appreciate the time you have spent helping me.

All the best

G

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Answer 5

GeMu00 Author

Level 1

8 points

Jul 14, 2020 2:29 PM in response to The_Knowledge_Seeker

Hi, thanks for the quick reply. It seems that he problem does indeed disappear in the guest account. In the main account it started flashing, and then I switched to guest for 5 minutes and there were no flashes - interesting!

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Answer 6

GeMu00 Author

Level 1

8 points

Jul 14, 2020 4:01 PM in response to GeMu00

Knowledge_Seeker, I don't know what this has done, but the blinking has stopped in my main account also. I was nearly ready to bring my Mac to recycling and invest in a new one but maybe I'll get another while out of it. Hopefully this cure is permanent - I will send an update tomorrow to let you know how it is progressing.

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Answer 7

GeMu00 Author

Level 1

8 points

Jul 16, 2020 1:19 AM in response to GeMu00

Update: Unfortunately the flashing started again, same as before reinstalling OS. The Guest account is now also flashing (it had started before doing the OS install). It took 2 hours to run the Disk Utility and Install in recovery mode, during which there was no flashing. Also there is no flashing in the Login screen.

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Answer 8

Jul 15, 2020 1:53 AM in response to GeMu00

Excellent!

If the problem returns, I'll consider other fixes for you.

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Answer 9

GeMu00 Author

Level 1

8 points

Jul 15, 2020 4:36 AM in response to The_Knowledge_Seeker

Hi, this morning it's all clear in Guest, but flashing badly in the main admin account. Quite quickly it seems to go to sleep and need power button to waken

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Answer 10

GeMu00 Author

Level 1

8 points

Jul 15, 2020 4:10 PM in response to The_Knowledge_Seeker

Thanks, I've done that. Looks OK for now but I will need to leave it for a while to see if it recurs. I will give you an update tomorrow. Thanks for your help with this!

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iMac screen flashing

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