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Modell A1312 / Mitte 2011 / 2,7 & 3,1 GHz Core i5 oder 3,4 GHz Core i7 Prozessor, ID iMac12,2

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identify iMac infinite reboot cause, psu, gpu, logic board?

Dear iMac lovers,

my 2nd hand imac keeps reboot to a un-usable degree since the start of June. i had bought it in June 2021 from an Indian couple.

During Feb-Apr, i turned on Quick Time, screenrecording for -100 hours over 12 weeks. the machine alum case was hot. suspecting, the last straw on a camel.

i connect my imac to external screen. surprsingly, the imac runs smoothly.

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my question is:

  1. is 4-hour QuickTime and hot alum case causing death on this old imac (27', 2011 mid, AMD radeon HD 6970m)?
  2. i bought a SSD to replace HDD, auto reboot still happens. My next target is: PSU? or GPU? (i will not buy any new/used logic board from any party because too too expensive. US $200-700. )
  3. how to distinguish failure due to PSU or due to GPU? the Samsung external display via mini display port cable runs smoothly. i guess PSU is at fault. because LED monitor consumes 40-50watt. my samsung external mon is powered itself, without relying power from imac PSU. is my line of thought logical, accurate and relevant?

Update (06/25/2022)

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Gfxcardstatus not running my desktop imac ...

The Diagnostic by apple only indicated absence of thermal sensor in SSD card at HDD bay.

The GPU AMD Radeon HD looks working...its temperature is 33 Celsius degree, more than CPU at 29 Celsius degree.

How to explain zero score in nova benchmark?

Thanks for Dan's insight .

Update (06/25/2022)

Hi Lemerise

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I had suspected the PSU too. Before delivering to technician for repair, i did check the parts on psu.

It looked normal on appearance .

But i have no relevant tool or schematic to check GPU performance , i eventually stopped my urge to buy new PSU. And just let a professional technician to discover what is happening .

I did buy a new wired keyboard when my imac started frequent breakdown. Before, i used a Bluetooth keyboard ,which is out of battery very soon in a few weeks time.

Maybe this wired keyboard is my last straw on a heavy camel. It puts extra, though however minute, irreversible an old powerhouse...

Will keep you, Dan and oldturkey3 posted of latest observations and discovery of my old machine repair status...

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6 Kommentare:

Sorry, I forgot the newer version of Gfxcardstatus doesn't work on the desktops.


Thanks Dan for your explanation anyway.

In the past week, i visited 3 technicians

*An online paid technician said, cannot fix online, should look at logic board, GPU, and GPU cable. Melt down logicboard.

*A free of charge technician, without physically checking my imac, commented: frequent auto restart is a sign of dying computer, should not repair. Further comment: should not spend on inspection at all, not to mention repair, because in depth inspection very expensive.

*I finally carried my imac to a professional technician for inspection and repair. Will let you the outcome hopefully in a few days.


@ninjasdu - I have a 27" 2011 iMac which is still running! I've had to replace the GPU once as I pushed the system a bit too hard. When Apple designed this system they didn't expect the rapid change in applications from limited graphics to some very high def stuff we are using today. The GPU this series had tended to out race what the system could offer for cooling.

This then gets to one of the issues diagnostics encountered as you replaced the HDD to a SSD which is an expected changeout but Apple had a custom HDD drive as they wanted to access the drives internal thermal sensor.

The long story short here is you need to install iMac Intel 21.5" and 27" (Mid 2011) SSD Temperature Sensor so SMC is able to monitor the SSD's thermals. Give this guide a review iMac Intel 27" EMC 2429 Austausch der Festplatte


Hi Dan

I did intend to find a thermal sensor for my new SSD in HD bay.

But in the end, i did not. I believe my repairman technician / vendor will eventually do so.

Because the frequent reboot situation remains the same , regardless of my new SSD instalment or not. Your guess is meaningful.

The High definition 4K on YouTube is a stress to a 2011 imac PSU.

Plus a wired keyboard as a replacement for Bluetooth keyboard.


Problem of DIY imac repair is:

*Lack of sufficient tools and sense and skills to diagnose and carry out repair. E.g lack of high resolution power to observe damage on circuit board, poor soldering technique.

*Without sufficient patience to buy different parts from overseas. Ebay, Amazon, AliExpress, taobao, Alibaba. And the quality of purchased items is a gambling decision, especially for an antique obsolete machine. Brand new parts from US is super expensive and unaffordable delivery charge, even after discount rate applied.

*Diagnosis sense / sensitivity to accurate diagnosis is not strong. DIY novice can only nonstop buy parts to testify his hypothesis. My purchase of new SSD to replace HD is a wrong move. My purchase of 5 connectors is a wrong move. My purchase of new soldering gun and multimetre is a wrong decision... Infinite buy of new parts and tools drain energy.

*Introduction of new risk and damage to an already broken machine. After i opened the machine, my screen fell down ...


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I would reconnect the internal display and then run the onboard diagnostics to see what it tells you.

Restart your system and press the D key to enter

Reference: Mac startup key combinations

I'm suspecting your discreet GPU has failed.

Diagnostics runs on the firmware driver for the Intel Intergraded graphics engine it has.

Your external display is able to run using the same Integrated graphics engine, but this time using the OS driver, as it we default to that.

You can also prove this using this great app gfxCardStatus

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Remove the unit power supply and check for faulty capacitors. It would not be surprising that a 11 years old PS needs a recapping. I just worked on this iMac model and even if the power supply was working there was 3 damaged capacitors. Top of the cap is doomed, its a sign the cap is failing soon or later.

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pmp calvin wird auf ewig dankbar sein.

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