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

Hi there - hope I'm on the right thread for this reply.

I recently suffered the same issue for over a week whereby my late 2012, 27" iMac (1TB fusion drive) would unexpectedly shutdown like someone had yanked the power supply cable from the back. I could only get it restarted by removing the power lead for 15 secs, plugging back in and waiting 5 secs before starting up - and apart from a Chrome "unexpected shutdown" message, you wouldn't have known that it had shut off.

I spent a few hours on to Apple Support trying various solutions (Diagnostic test, MemTest, SMC/PRAM resets, Sierra reinstall etc).

By trial and error, I eventually identified the problem's source as being my Satechi 7 port USB 3.0 hub which had 2 x Porsche design (1TG and 4 TB) external HDD's attached, along with 2 x charge/sync docks for iPad and iPhone. Since I removed the USB Hub and plugged the peripherals into the back of the iMac, I have had no issues whatsoever - and my pride & joy is back working like a dream.

I hope this update helps

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.

Jul 5, 2017 9:19 PM Re: 27 iMac (2012) crashes and requires smc reset to turn onin response to Lagoiski

I also have this problem.

Is there anyone who has installed a LiteOn power supply who is still experiencing this issue?

Hi Bill,

well, almost 9 months after my PSU replacement to the Lite-on, and the system is still running. I can't even remember when I last made a full shot down, so it's working as it should.

I think the replacement was a bit complicated (first time, and thanks fr Youtube), but for a authorised repair person, I assume the PSU repair is straight forward and won't take long.

Leo

I had my late 2012 iMac in several times over many, many months with no solution because they could not replicate the issue even after keeping the computer sometimes running for 2-3 days. The problem got worse and worse. Finally, it did fail there and the Genius Bar concluded it was the entire mother board. After some very unhappy back and forth over quality and what I and they should be responsible for regardless of age, they agreed to cover half the cost. I had it replaced about a year ago and it has been running flawlessly ever since. It was either that or buy a brand new unit, which I did not need. This is definitely a common defect in this run of 2012 iMacs...

It's the identical fault and thanks for your solution.. Hopefully that was it. It can be a cause but my feeling is the non Liteon power supplies are not 100%. I bought a new Liteon from eBay got it replaced by a tech and that is the only thing that solved it. The issue is however intermittent for many. In your case, if it does return, which I hope not, I suggest finding a Liteon supply.

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.

Sad to read that, .. but keep in mind something, YOU are the customer, you will pay the service,, you MUST to claim your rights, they MUST to listen to you, is really blind that they won't to see this large thread on the official Apple site....

Here is how to reproduce the problem: Just keep the imac power off and connected to power supply for a couple of hours until the bad capacitor of your PSU get charged, turn on the iMac (at the store).. and wait with them there until it shuts down.. then, lets see what they can say...

Don't allow they ask you for change the Logic Board... you need to tell them to change the PSU first.. and try. you know.. everything you do in an Apple Store is $$..

Good luck

Mine has been running faultlessly since fitting a LiteOn power supply's I am pretty sure you will solve the issue with one.

I have this same problem with my late 2012 iMac 27”. Took it to apple in SoCal and got power supply unit and logic board replaced. Now three months of no problems so far.

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!

Add another victim to the list for this problem. Late 2012 iMac 27". A month or so ago my wife start complaining about her iMac just shutting off for no reason at all, then not being able to power it back on. This unit has been plugged into a APC UPS since it was originally purchased. As with numerous other posters in this thread the only way to reset the iMac is to pull power and let sit for a few seconds. Sometimes it requires pulling the power cord a second time. Very surprised to find the number of people that have had this problem here. To think how many hundreds more just take theirs in to get it fixed without reporting it is somewhat disturbing.

Since I don't have an Apple store nearby, I have decided to just order a replacement power supply from an Amazon seller. Description says it is a Lite-On model so fingers crossed. Just wanted to make sure to report here to add to the documentation.

Just for info here. I just replaced my power supply with a LiteOn. Too early to say, but no issues yet. Before, it was shutting down every day..

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.

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.

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?