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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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iMac mid 2011 27" wouldn't stay off, now kernel panics & rnd shutdowns

my imac started having an issue about 6 months ago where it wouldn’t stay turned off, later it started having an issue where it kernel panicked randomly, then it started powering itself off and then due to the previous issue it would turn itself back on of course, I’m suspecting the power supply but all 12v lines test as 11.97 with the machine powered on with no display attached though its not a really an under load power test it seems OK 12v wise? the pram battery seemed a bit weak though it was holding clock but i replaced that, It does have the 2GB 6970m graphics card with a DHJW serial number but were now in 2019 so apples extended warranty program on that card is no longer applicable (was only for 3 years after purchase ;( ).

Though I didn’t really notice & have had any graphic corruptions in 3d use, but I didn’t use the graphics card intensely on this machine, I did run allot of peripherals, 2 external monitors a thunderbolt dock with attached USB3 drives etc, though that dock has its own power supply? I think one ram slot/stick became dodgy at one point so I removed a ram stick, Next I’m going to next conduct an AHT test on it, though it has stopped turning itself back on since opened for testing and after I replaced the BR2032 pram battery with a CR2032.

I Guess many might say getting 8 years from it is doing well, but TBH I don’t expect anything as lightly used as this machine to fail? I’ve got computers from the 80’s that still work fine. a capacitor here a capacitor there everything’s fine etc, I suspect there will be very few of these imacs in working order in 10 years from now, working models maybe rarer than hens teeth?

If anyone has any other sensible tests or suggestions I’m interested, don’t suggest power in the house as its never previously been an issue and tests fine with a tester.


I'm adding my updates as to what ive tried to keep a note for myself and to keep others updated, additional steps ive tried>

I ran AHT 3A222 in normal testing mode and it showed a memory error I had two 4gb crucial simms and 2 x 2gb elipida dimms which were not showing errors before, but i had previously had to remove two 4gb simms in the last two slots bringing me down from 16GB to 12GB as it didn't seem to like to operate at 16GB memory the simms were fine in another machine methinks, I took out the two 2gb elpida simms bringing the memory in the imac down to 8GB's total two 4GB's simms in two slots.

this resolved the memory error in AHT, i then got a sensor error but thats because I'm testing with a 64GB ssd in the hard drive slot so the sensor error i believe it relates to the imac not being able to detect hard drive temperature. so i don't perceive that as a big issue, as the problems were occurring with the original hard drive which it could detect temp on.

never crashes when running AHT

anyway i then attempted to boot of one the SSD partitions into 10.10 it gets a third the way across petrol gauge wise, the screen gets brighter a bit as a bit to move up a gear in the boot process and then it hard restarts on me.

I then tried to do recovery mode install which boots up but doesn't make it to the installer without hard reset-ing in a similar way

I then also tried internet recovery mode it operates fine whilst downloading a full installer, then I begin to boot the internet recovery installer, it gets to the skuomorhpic textured background of the installer like its going to allow me to install then it does a similar black screen off hard reset and restarts.

now running AHT in extended mode

Update (05/10/2019)

I've owned this machine from new and do apple technical support for a living, so no boiler plate rubbish replies like one sees on the apple support forums pls cheers.

Answer this question I have this problem too

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What does your tempitures look like? Install this app TG Pro try to run is as long as you can. Paste a snapshot of the main window (likely will need to resize it so all the sensors and fans are visible) Adding images to an existing question


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As much as you don’t want boilerplate answers… It’s the solutions to the symptoms is about all we can offer.

Restarting/rebooting systems are always hard to isolate the root cause so you end up working off a list of suspect issues unless you can get diagnostics to help focus your hunting.

Given the systems age you could have a bad GPU board. The heat sink could be failing or the thermal paste is in need of refreshing on both the CPU & GPU. These are the easiest to fix.

The logic board is more suspect then the power supply in my option. Here the VRM’s are likely failing. You’ll need to get the schematics and walk through the voltage measures.

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