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Model A1312 / Mid 2010 / 3.2 GHz Core i3 or 2.8 & 3.6 GHz Core i5 or 2.93 GHz Core i7, ID iMac11,3

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It shutdown and never came back

As I was working on my Mid 2010 27” iMac, the screen changed with strange graphic artifacts. I shut it down and after a min when I tried to power it back on again it just wouldn’t start.

When I pressed the power button I could hear the fans starting to work but after 5secs they stoped. No chime was heard, nor would the iMac boot. Screen remained black.

I was working with High Sierra. Maybe I’m lucky that I got a TimeMachine backup, but I have no clue what my next step can be… I’m totally lost ?

PS: Supposedly if I buy a new, up to date iMac, can I use the TimeMachine backup I have from High Sierra system to restore my old iMac stuff on the new system?

Update (09/06/2021)

I did a few things: Removed the Display and GPU (Didn't remove the GPU temp sensor)

  • Did a PRAM reset
  • Fans worked at high speed
  • Heard the Chime once

Then I placed the GPU back and at boot there was a continuous chime. Strange because if its the GPU causing the continuous chime, why wasn't it there in the first place, before I opened the iMac and before I removed/connected the GPU?

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That still makes sense! Once your system fails it will set a latch to prevent you from restarting as SMC will prevent it. Once you disconnect the power cord and break the connections to SMC. SMC will reset which is why your system now has a different reaction.

Time for a new GPU board. Make sure you get a real Apple unit as they have custom firmware on them,


Thanks so much Dan... just a few unknown words... latch? SMC?


Latch - A logic toggle state, in binary we talk about 0 - Off/1 On states which is how computers work! Here like HDD/SSD's a state is stored, here this state is held in a small area of SRAM in the SMC chip.

SMC - System Management Controller; The chip which takes care of all of the power & thermal aspects of the system to make sure everything is working correctly.



Also, is there some way i can double check that a new GPU board is needed? Or is this a clear cut case? And if i find a new GPU how can i know its a real Apple unit? Some specific code to look for? Or some link for purchase u have in mind so i can see the specs perhaps?

Once I get a new graphics card and I install it, will the continuous chime sound stop, or must I do something specific for it?


@genik - Other than replacing it there is no means to check it. You might be able to check your system by using a USB wired keyboard forcing the system into Target Disk Mode. This bypasses the last part of POST using the systems BIOS (EFI) to boot up under, here you will see an icon on your display as the internal graphics engine in the CPU will be active. IF that works then you know it's the GPU board, but often the GPU board failure can be in a state that prevents Target Disk Mode so don't depend on it as an absolute.

Restart your system and press the T key to enter

Reference: Mac startup key combinations

Here's one source that offers the needed part 27" iMac AMD (ATI) Radeon HD 5670 or Radeon HD 5750 GPU boards


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Yes, your TimeMachine backup will still work with a replacement system.

But! Depending on what Apps you currently have you might have issues as the newer Catalina and newer won’t run 32bit apps.

You might want to look for a used Intel Mac to replace yours

Update (09/07/2021)

Is it Christmas! The light you are seeing though the RAM slot area are from the onboard diagnostic LED’s. Most of the time they are covered!

Block Image

And here’s what they look like and ID’ed

Block Image

And here's a breakdown of the onboard diagnostic LED's:

LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty.

LED 2 - Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

LED 3 - Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.

LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.

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Thanks Dan. This issue I’m having, does it look like it’s one that I’ll need a replacement iMac, or can it be something that could be fixed?

What can I do regarding fixing?

One more thing is that, underneath, next to the memory modules, I can see 3 green led lights when I power on the iMac. And when it’s powered off, only one led still remains lighted.


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genik sarà eternamente grato.
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