Model A1311 / Mid 2011 / 2.5 & 2.7 GHz Core i5 or 2.8 GHz Core i7 Processor

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Why is my display flickering after this repair?


After completing this DIY, I am seeing occasional (2-3 times per minute) flickering / dimming of the iMac display. It happens for ~1 second and only dims the image; the screen does not turn off completely nor is there any distortion of the image. I can post a video if that is helpful.

I was pretty careful to ensure the display cable was properly secured, and the screws holding the display in are uniformly snug. (I saw some reports for earlier iMac generations that suggested display issues could result from improperly secured screws.)

I should mention that I undertook this upgrade shortly after buying the iMac used, so it is possible that the issue was already there and I didn't notice it before beginning surgery. But I had used it for a few hours and never saw it, so I'm skeptical that the problem existed before the upgrade.

Any ideas?


Tried removing the display again, re-seated all display connectors, reinstalled display. The issue persists.

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Please see this Screen flickering and (some times) dimming. Methodically check/eliminate possible causes. Most common: connectors that aren't (connected properly that is) nicked/damaged cable where vibration can cause signal interruption or shorting.

If this Answer is helpful please remember to return and mark it Accepted.

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Turns out I neglected to re-connect the vertical sync connector cable on the monitor in Step 5: iMac Intel 21.5" EMC 2389 Dual Drive Installation

Thanks for your help!


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Beppe will be eternally grateful.
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