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Modelli A1419 / Fine 2012 / Processori 2.9 & 3.2 GHz Core i5 o 3.4 GHz Core i7, ID iMac13,2

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Shuts off. Won't Power On Until Power Cord Pulled and Re-connected

I have the subject iMac and I’ll be a bit more expansive about the subject title:

While using the machine (usually Lightroom Classic), it will occasionally power off spontaneously; not a “shut-down” but as if the power cord was pulled. Additionally, when just left alone for a while (could be in LR Library or just at the Desktop), the same “power-off” can happen.

But here’s where it gets a bit stranger: Pressing the power button will always fail to startup the iMac after such a “power-off”. I have to pull the power cord, wait some seconds, then plug it back in whereupon a press on the power button will start it back up.

I’ve tried resetting SMU and PRAM but the problem remains. I’ve tried using Macs Fan Control to manually keep everything cooler and even set LR to not use the dedicated GPU. I think this has worked so far (but not failing isn’t confirmation of anything).

Suggestions appreciated. I am not adept at opening up this model but if there’s some diagnostic one would suggest, I’ll try it.


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Sounds like your system is overheating! Depending on the size of your Lightroom project it maybe too much for your system in its current state.

Over time the fans and the heatsink fins get clogged up with dust and other debris, the more choked up the less cooling, SMC will shut you down once you hit the limit of the systems cooling.

So to start with I would install a good thermal monitoring app like TG Pro is it by far the best out there! In your case you’ll want the full package to gain the logging. Now start monitoring! Hopefully you can get the system to wink out, but this time let the system cool down and see if you can restart it by pressing the power button lightly (like you would if in sleep mode) If you can do that your data should be saved and you can review things from the log. Post a screenshot if you can when your system is toasty so I can see the sensors and the fans RPM. Do make sure you capture all of the sensors you may need to grow the window to get a single snapshot or take two after sliding the window down to get the stragglers following this guide to post your captures Aggiungere immagini ad una domanda

I would also run the onboard diagnostics as well. Restart your system and press the D key to enter. I don’t think you’ll get an error but its a good idea to check.

OK, we’ve talked a lot about diagnostics so far and getting start point of your temps now.

So what to do to fix this? Assuming you have a dust issue you’ll need to open the system to clean things out. Get a small soft paint brush as well as can of can’ed air with a snorkel as you’ll need it. Here’s the guide to open your system follow this guide to the letter! Sostituzione ventola iMac Intel 27" EMC 2546 you’ll also need a special tool to cut the adhesive tapes which holds your display on which is part of this kit iMac Intel 27" (2012-2019) Adhesive Strips and you may want to get a second set of tapes just in case. I also find these helpful Plastic Cards I would get two sets (four). Using some cardboard you can make this or just order it as well [prodotto collegato mancante o disabilitato: IF145-224-2] to hold your system in place as you work on it

And lastly, I recommend getting a small J roller and variable temp heat gun or hair drier as you will need the pressure from the roller and the heat from the heat gun to help set the adhesive so the screen is properly attached when you’re done.

But before you go into your system lets make sure we are are the right track.

Immagine Plastic Cards


Plastic Cards


Immagine iMac Intel 27" (2012-2019) Adhesive Strips


iMac Intel 27" (2012-2019) Adhesive Strips


Immagine iMac Intel 27" EMC 2546 Ventola


Sostituzione ventola iMac Intel 27" EMC 2546



1 - 2 hours

Immagine iFixit


Aggiungere immagini ad una domanda


Molto facile

2 - 5 minutes

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4 Commenti:

Agree that it seems excessive temp may be a/the problem; hence, my installation of Macs Fan Control (MFC) and manually setting the CPU max temp to 129F which, under normal circumstances, is laughably low. Since I've done that, however, the system doesn't power off by itself.

One other symptom (or, rather, display of a symptom): When I last used the iMac in late May, I shut it down gracefully then powered it up normally (just to make sure all was okay) and shut it down again. This was after I had installed MFC and told LR Classic to -not- use the GPU card (and the spontaneous shut-downs seemed to have stopped). This evening (prior to my initial post here), when I tried powering up the iMac, it would not; I had to unplug the power cable for about 5 seconds and re-plug it in order to get the power button to respond (the same symptom after a spontaneous power-off).

So, if the unit shut down gracefully (and was able to power up immediately using the power button -then-) but, after three weeks of non-use (but remaining plugged into a known-good UPS) it requires the "unplug/wait/re-plug" procedure, would this not indicate some sort of SMU/firmware issue rather than just heat?

I'm going to hold off on the TG Pro for the moment as MFC is keeping things cooler.

As this is an iMac, one would not expect to see a motherboard Intel GPU is present (but it is) so requiring LR Classic to use it (and not the video card) may be helping to mitigate this issue. Maybe the video card is failing, as well (although I have not seen any video artifacts).


@rumplestiltskin - Nope you have a heat issue and your slowly cooking your system! I love slow roast coffee, not iMac's!

Time to bite the bullet! Given the GPU issues I would also redo the thermal paste on both CPU and GPU.

I love free! But are you cheating your self using a weak diagnostic solution and expecting it to fix the underlying issue? Shutting down your discreet GPU really doesn't help you as well.

I really don't like Macs Fan Control as I've seen too many issues with it. Between not working properly on some systems, memory leaks and not as easy to understand what's happening and lastly it doesn't log! TG Pro is maintained aggressively! Not true for MFC.


I do appreciate your advice, Dan but this iMac is almost 10 years old and if I can nursemaid it through a few more months, I'll be replacing it with a new PC.

Though I was a Mac consultant and repair person for most of the last 25 years, once Jony Ive pooched the iMac design (ie, double-faced tape for the screen, non-upgradeable most-everything-else), I fired Apple and retired. I've seen two Apple-certified techs crack iMac screens during the removal process so I declined that task for clients and sent them to Apple where, if the screen was destroyed, at least it would be on Apple's dime.

If one can live with the increased fan noise, I've found MFC to work perfectly. Agreed; it's not a solution but does manage to keep old, otherwise marginal Macs running until the owner buys a new machine (either Mac or Windows).


I did mark your post as the answer (because it was complete and accurate). My earlier comments do not dispute your answer; I just am using a kludge until the iMac shuffles off its mortal coil. :D


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