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Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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Why does my iMac restart randomly?

My iMac has been restarting randomly for several weeks. The screen jumps to black and the Mac restart with the familiar Apple Start tune. If the iMac starts cold, the chance of a random restart is higher. Once it has been switched on for a while, the machine works normally. But even then it can happen that the iMac reboots suddenly and randomly. In short: you can not trust the machine.

To be sure, I have done a clean reinstallation of High Sierra. No random restart during installation (s) from USB stick.

NVRAM / PRAM reset done. No improvement.

SMC reset done. No improvement.

± 3 years ago I have already provided this iMac with a new VGA card by Apple because of a well-known problem Apple recognized. So I think the chance is small that there is a problem there.

Apple Diagnostic Tool done, normal and comprehensive. No errors were found, not even in the RAM.

It is an iMac 27 '' Mid 2011 EMC 2429 / A1312 with Intel (Quad) Core i7 3,4 GHz, 4x4GB RAM and 250GB Samsung Pro SSD.

My big question: What is the defect that "sometimes / regularly" the restarts arise?

My guess is that the Power Supply needs replacing. However, why do I not suffer from the problem during installation.

On the internet I come across the same issue a lot, but nobody provides a clear solution. Hopefully there is an expert here who has already got experience with this issue.

Beantwoord deze vraag Dit probleem heb ik ook

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Hi Cees, ik ben bang dat je gelijk hebt als je zegt;

My guess is that the Power Supply needs replacing. However, why do I not suffer from the problem during installation.

Vrij eenvouding, tijdens de installatie word lang niet alle hardware volledig aangesproken (Videokaart word bijv. wel geïnitialiseerd maar geen KEXTS geladen.) Maw. bij een installatie word lang niet zoveel stroom verbruikt.

Het “recappen” van de oude voeding moet dit probleem oplossen.

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I have a late 2009 A1312 with the i7 and has the same issue. Random sudden black screen and reboot.

I tried changing motherboard and WIFI-board with no improvement.

What must have helped was when I removed the motherboard, cleaned all connectors to it with electronic cleaning spray and reassembled it. So my guess is bad cabling in my case. The IMac is now old. So it makes sense I think. Now it is stable again. Even with Catalina. Done with dosdude1 patcher.

Updaten (16-02-21)

I found the problem. It is the RAM that had some bad memory modules. Change one at a time and run with less RAM for a while to see if the problem perisists. I have tested the RAM with a software test earlier without any problem. So I guess it is a sporadic problem.

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hello Cees

I've had about the same problem, but not with a Mac but with a normal PC.

The problem was a faulty powerplug on the CD player that sometimes caused a short circuit.

I suggest, as Krister puts it, that you take your Mac apart and clean the individual circuit boards with compressed air.

Also replace the paste on the CPU heatsink,

Replace the hard drive just in case.

And perform a full reinstallation.

Succes;

Homer82

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ever checked if your CMOS battery is still powerd? mabey that makes it reboot idk how mac exactley works. but that did it for me once.

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Cees Hoek zal eeuwig dankbaar zijn.
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