27 iMac (2012) crashes and requires smc reset to turn on

I figured I"d jump in for the record.

Late 2012 27" iMac i7, 32g ram, 1TB Fusion.

A little different from others who said the problem started gradually, mine system has run perfect for 39 months. And now, conveniently 90 days outside of the 3-year warranty shut down in the middle of using Word.

Couldn't turn it back on.

Tried SMS reset, etc... nothing seemed to work...

waited an hour and decided to give it a go on a different outlet and turned on as if there were no issues. Ran an extension cord and set it back up on my desk, ran for about 15 minutes and boom. Shut down.

After chat support, they said to reinstall OS... in the middle of OS reinstall it shut down. I gave up. I suspected motherboard or power supply, and this thread seems to confirm it.

Have an appointment today at the store, we'll see what they say, and see if they have any mercy only a few months out of AppleCare.

I was always a PC until I purchased the imac. Since I've purchased a MacBook Pro, ipads, iphones, watch, etc.

If this was a PC it would take me 10 minutes to throw in a new power supply and I'd be back to work. All my fears are realized, I'll end up with a $3000 brick. No PC ever cost me $1000/year to run. If Apple can't help, I will order the Lite-On power supply and take a whack at it, the most I have to lose is the price of power supply.

Thanks for all the insight here. I'm surprised Apple won't launch a repair program for this being it seems so specific to late 2012 i7 imacs.

Just an update on our iMac. Ordered the replacement power supply from Amazon last week and installed over the weekend. It was in fact a Lite-On branding. Everything went without a hitch and the iMac has been on non-stop since. Purchased the OWC kit as well which comes with tools and the adhesive sets. The adhesive set was spot on. For those a little uncomfortable with replacing the power supply have no fear. If you have the ability to change a power supply on a regular PC, you will have no problem with this replacement. Just takes a little more time.

Same happening to my late 2012 27in iMac. Happens randomly, sometimes not for hours, sometimes after a few minutes. Unplugging for 10 sec gets it to reboot. I'm thinking when it blanks out that it's actually not loosing power, but going to sleep.. maybe why only unplugging it and plugging it back in forces the reboot. The first time it happened I blew into the vents and a decent amount of fine dust clumps came out the bottom vents. Since then I've sprayed compressed air into every crack I could to get out all the dust I could. I fear I may have also packed some dust in places.. perhaps that's causing the heat to rise quickly in sensitive areas?

Can I open the back of the iMac myself, or do I need to take it in to an Apple Store?

My humble suggestion: once you open the unit, everything is on you. Instead first make a Genius appointment... Take it back to the Apple store, ask to speak with the store manager and show him this thread and how many have had the exact same issue. Be firm with Apple because this really is BS! I was nice but clearly I was frustrated after numerous trips in. My settlement with our store manager here was that I would pay for half the repair. What they found was actually changing out the motherboard as the cure. It worked!! It was not the power supply. I went down this road. It's not a heat issue as even on cold days in my unheated office it still would quit. It's a motherboard issue in most cases.

I had the logic board replaced by Apple but the issue still happened again - almost immediately.

Apple replaced the power supply and the problem was fixed for about 6 months, and it was tolerable to work with (I got about 8 hours work out of it in one go) for about a year.

Now it's back to cutting out again after a few hours.

Apple Store looked at it again and ran it non-stop for three days. Suggested it is an external hard drive. It's not.

PC store ran it for 4 days without a problem and suggested it was probably best not to just replace the power supply because an internet forum suggested it, as I had requested. I agree, but I will try anything at this point! They suggested i needed surge protector. I got that. Change position of Mac in house. Did that. I took the Mac out of that location altogether, in case my house electrics are faulty. After all of these it still did it again.

The sensible solution would be to wait a week for my genius bar appt, take it to the store again, wait another week to find them saying there is no problem and insist the thing has a fault and insist they fix it ... but i have run out of patience and time and am trying a different PC repair shop.

Then if it fails again, I have to decide whether to get a new computer and whether it will still be Apple after all this carry on.

Just an updated. Picked up my Mac from Apple yesterday. They claimed issues were resolved with reformat and reinstallation of software.

I’m doubtful this will hold, but will give them the benefit of the doubt. They were able to replicate my issues, but then after reformatting the system and reinstalling OS (leaving me to install the updates and get back to current), the system is stable at the moment.

Seeing these stories scare me, I rely on my machine for production work and the experience has shaken my confidence. Any computer can malfunction, but it seems like a bizarre issue to be related software. Furthermore, I had it crashing resetting the PRAM - which seems (please correct me if I'm wrong), is a function being executed during POST (prior to the OS loading).

The PRAM crash does not occur at this time. I'll keep you folks updated when I have the opportunity to get a full day in on it and run it through its paces.

Apple seem to replace with the power supply that has issues.

In general if a LiteOn power supply is used, the issue seems to go away. Of course, some computers have issues anyway, but in this case, the large majority of people who solved the issue used a LiteOn PS. Apple don't seem to in general. Wether this helps, I don't know!

Update: My repair guy replaced power supply with liteon brand. The power supply blew. He's ordered another in case it was a faulty one and will try again next week. A few days ago he replicated the fault at his desk and diagnosed 100% it was the power supply which I was overjoyed to hear. So this is a real disappointment. He also wonders if it's the logic board (the new logic board, now only a year old). I feel most depressed about this whole saga. I have work to do and will probably end up getting a new computer when I can least afford it. After 20 years using Apple Macs, I now don't trust them any more.

Hi, these days I'm having the same problem.

My iMac (late 2012 i7, 32gb ram, fusion drive 1TB) shuts down randomly with no apparent reason.

I looked some threads on the apple support community with no help.

The computer shuts down in idle and in full load situations.

Even when I'm using windows 8 with a boot camp partition.

I called the Apple support and they told me to do a full hardware test ( hold D on startup ).

It took a while (about 3 hours) but it was clean.

The guy who I talked with told me to do a clan install of the system in case the hardware test was clean. Maybe it is a software problem ( oh yes he checked the caches and .plist file too)

If it persists after a clean install I should take by mac to assistance to be checked and repaired if needed.

I'll contact the support again on Monday GTM+1 time because I had a shut down even using windows...

I guess (unfortunately) it's some hardware problem....

Hi, same problem.

My 27 iMac i5 2012 shuts down randomly, for restart unplug power line for 30 seconds, (reset SMC).

After hardware test (ok) reset imac with clean install but never same problem.

how your have resolved.

think apple support say.

THANKS

Hi, in the end I brought the computer to the Apple Store and they changed the power supply.

It wasn't a software problem.

It was on apple care so I did't pay, but i was around 70€ I think.