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Model A1419 / Late 2012 / 2.9 & 3.2 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac13,2

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iMac bootup and display issue

Specs: Late 2012 Imac 27”

  • Intel i5 2.9 GHz
  • NVIDIA GeForce GTX 660M 512 MB

My colleague was having issues with this machine. Initially upon boot up, he was presented with the standard white screen, Apple logo, progress bar.

However, the progress bar would get to about 40% and would get stuck. Furthermore, the screen is covered in flickering pink/green lines which makes it difficult (but manageable enough) to read the screen. I have tried booting in safe mode, recovery mode, resetting NVRAM/PRAM, diagnostic mode, verbose boot, and booting to a separate USB with a fresh Catalina install.

Every key combination I’ve tried will result in the same white screen, Apple logo, and progress bar, which is able to load up to a different % before getting stuck (other than verbose boot, which I am unable to read any console output due to the screen issue). I decided to replace the SSD and inspect the internals for any visible damage. After removing the screen and replacing the SSD, I booted up, only to be met with the same issue.

I unplugged the Vertical sync and LED backlight cables again to ensure I had installed the SSD properly, and after booting up again, the screen won’t turn on (Completely black with no backlight either).

I inspected the vertical sync and backlight cables and saw no physical damage on them.

I also tried connecting to an external display using a Mini DisplayPort to HDMI adapter, which also did not work.

Furthermore, the bottom 3 onboard diagnostic LEDs still show that the computer is “Functioning properly” despite the screen not working.

If anyone has any experience with either of these issues (Boot Up issue or screen issue) or has any advice I would truly appreciate it

Answer this question I have this problem too

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Your GPU is/has failed. It appears this GPU is integrated into the logic board from this guide:

iMac Intel 27" EMC 2546 Logic Board Replacement

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Are you sure? It booted fine before I disconnected the display cables for the second time. It would be a bummer if so

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Your clue is the flickering pink/green lines, and the fact that an external monitor will not work.

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Hi did this ever get fixed? My issue is a thicker black vertical bar and a thin red one. I am wondering if this cable will fix that: iMac Intel 27" EMC 2546 & 2639 Display Data Cable. Thx for any help!

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No this did not get resolved. If a new display cable solves your issue please let me know!

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@mikerotch - Your issue is a bad GPU as Mayer described in his solution this is a common issue in this series. It often happens on systems which are pressed hard with graphical applications like gaming, image and video work.

@herojig - Your issue is a bad LCD panel a very different issue. This can happen due to a physical bang, damaging the LCD panel during repair and lastly during manufacture.

All three are related to the flex cable attachment to the glass LCD panel. We call these problems TAB errors. Sadly, there just isn't any repair other than replacing the display assembly.

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shankar will be eternally grateful.
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