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

I owned many assembled pc in my life. power supply is a fragile component also in PC. i changed several psu in my past pc. also in imac is the same problem. but in the PC is very simply replace them. in new imac the PSU is more expensive and difficult to replace it. this is the real matter. but we can't consider trash the imac only for the psu. because also in pc there is the same problem. it is like consider trash a car because the breaking pads need to be replaced every 20.000 miles.

But apple have to do somethings for the Delta psu. because they are not good

As I posted earlier, my liteon power supply continues to work great after replacing the delta supply.

I see people posting that the delta supply is bad and the liteon is good. How do people know that the liteon won't fail in 3 years. My imac lasted 3 years with the delta and worked fine. Has the liteon been around for 3 years. If someone has tested these supplies against each other i would love to see the results. I would not leap to the conclusion that the liteon is better.

Wow. 32 pages of replies to this problem and I'm adding another to the pile.

Same problem on a late 2013, 27" iMac. Only starts up after being unplugged for a time. Like others have said the longer it's unplugged for the longer it seem to run. Average about 10 minutes after being unplugged for 12 hours. It then shuts itself off as if the power was lost. Sometimes I'm able to restart for a few minutes. Have started in Safe Mode, reset the SMC and NVRAM with no change. Added another Admin user and logged in with that and same result.

This computer is new to me having bought it used. Had very little use and I trust the seller. There may be a lesson here but I'm still praying for a simple solution but as time progresses I fast loosing hope. Have a Genius Bar appointment for next week. Investing a bunch of money in it won't make sense to me. Should have bought new or not at all. No AppleCare at this point.

Don't be too concerned....I'm convinced it's a Power Supply issue, that is very cheap to fix by Apple.

The only problem is I think Apple are using the Delta brand power supply which are prone to issues. so I have had 2 replaced in the last 3 months.

They put a new one in last week, and so far no shut downs. But they couldn't confirm what brand they put in for me.

Apparently the Liteon brand seems to give people no issues.

So a (hopefully) final update from me on this thread. I've posted before on here but it's been a while - I've had the same problem as everyone else.

To date my iMac has had it's HD replaced (under the fusion drive replacement program last year), two power supply replacements and finally a complete logic board and airport card replacement just last month. None of these fixed the issue and now finally to their credit Apple have offered to replace the computer. Not bad service considering it's coming up on 4 years old.

I did mention about the different brands of power supplies but unless you can speak directly to a senior engineer they're not interested.

I hope this gives some hope to anyone still suffering with this problem. Go through the Apple store process and once they've seen that the problem persists after three or more hardware changes they should feel obliged to replace the unit. It's a pain while it's happening but it has resulted in a brand new iMac for me.

I too, have had the exact same problem that everyone here has had. Late 2012 i7 27" iMac, purchased March 2013. Problem started a year ago. Went to Apple genius, got diagnosed as a software problem. Reinstalled all software, worked for about a day, then started all over again. Reinstalled software repeatedly, seemed to work at first, but after a day or so, the problem reappeared. Nothing seemed to work, so took it into Apple authorized repair shop, and they diagnosed a motherboard issue. I don't think so. We will see, and I will let y'all know what is going on with it.

they changed all these parts because they don't know that the problem is the Delta PSU.

probably they relpace your psu ever with the delta one instead LiteON.

but you have an apple care of 4 years? or you had to pay for all this replacing?

Ok...update.......

Back to the drawing board....after my second PSU replacement at the Apple Store everything was going great, until one morning my iMac wouldn't start up.

So I had to unplug it and plug it back in from the back to reset the SMC and it still wouldn't power up. I have to leave it for quite some time unplugged at the back, then plug it back in, then it powers up.

This happens continuously now. After using it, when I power it off and leave it for a few hours and then try to power it on, it won't start up unless I unplug and leave it for a while.

I've also had one shut down in the middle of doing something.

This is so annoying, and reading through this thread lots of people have experienced the same issue/s.

So It's back to the Apple Store again for me next Monday.

I'm not sure what they are going to tell me, as they did every test under the sun and said it's perfectly fine. But they did replace the PSU for me a second time which worked for a couple of weeks then back the issues again.

I started thinking simply about this and thought is it just my power cord....but it doesn't make sense that it is, as it powers up and stays powered on for quite some time..... so that can't really be the issue.

I bet next they suggest a wipe of my drive......I'll keep you updated.

Update here. Well I took the advice of a few key users and said screw it time to attempt the fix on this expensive paper weight. Amazon had the Liteon PS and installed on Oct 15th and put machine back together and have worked it like a "rented mule" since with no shut downs. Thank you to the members who listed the parts etc. Few side notes for users who may attempt this repair which is really not that hard if you follow the directions and work slow. This is without a doubt a Delta PS issue in my mind.

• Be super careful with the small plugs on ribbon cable for display. They are the most fragile plugs in this repair and don't take much to bend or break them. Use light pressure to plugging back in and flip small clasp with black ribbon over connection thats it. It may appear it's not seated but it will be.
• On the speaker the small black cable that runs from the PS along side of speaker and down to power button is very fragile. Make sure to run it back in the groove that is on base of speaker that goes and tucks back in above the power button. I actually broke the one on my unit and I had to remove power button and re solder it which was "special" trust me no fun be careful here.
• Make sure to handle the screen with great care. This is the most important part of the job in my opinion. Slowly run a guitar pick around the glass making sure not to push too deep into the gap 1/4" MAX and remove the adhesive. Extra care around camera at top and also along base after screen is lifted slightly.

If you have any questions feel free to ask. 🙂

Thanks for the update and the tips on installation.

Just to update everyone on my situation.

I took my iMac back to the Apple Store a week ago. I saw a guy at the Genius Bar and explained I had been here twice and had 2 power supplies replaced and my iMac was still shutting down. I then mentioned this forum again and that I think it's it's the brand of Power supply. Like usual they didn't want to know about it and said I was thinking about this very two dimensionally.....hmmmm......

After explaining all the issues I had been having he was kind of stumped and then said we need to change the Logic board.....he said because I have had a bad experience and have been mis diagnosed twice he will talk to his manager about this. He came back and said they will replace the logic board for free. Thank heavens. there was no way I wanted to pay $800 for it.

Anyway, to cut a long story short, I picked up my iMac, and the next day with a new logic board and decided to try it out....and within 10 mins it shut down randomly. I was so ****** off. I had to do SMC resets every time and it kept shutting down about 5 times that day. I was so over it.

I called up the Apple Store and spoke to the manager....he said to rule out a software issue I should do a clean install of the OS. I said I could do that myself. I was annoyed because I really didn't want the hassle. Anyway the issue was that i couldn't download Sierra from the App Store to create a bootable drive because my iMac kept shutting down.

I just forgot about it till the next day as I was over it. Anyway, the next morning I tried to down load Sierra and my iMac shut down. I was livid at this stage.

I then did another SMC reset.....and guess what..........

My iMac has behaved itself since. Not one shut down...it's working as normal.

I downloaded Sierra...I also did a full Clone backup over 1 1/2 days with not one shut down.

I am left scratching my head over this.

So for now it's behaving and working fine. But I'm just waiting for the next shut down.

Hi guys,

I can't believe I read a 48 page thread on my iPhone. Let me explain my similar situation:

I purchased a late December 2012 27"iMac in Singapore which arrived in February:

Specs:

3.4GHz quad-core Intel Core i7 (Turbo Boost up to 3.9GHz).8GB of 1600MHz DDR3 memory1TB Fusion Drive

NVIDIA GeForce GTX 680MX with 2GB of GDDR5 memory

I purchased the upgrades because like many people I wanted a machine that lasted me 5 years. I'm heavy into wedding documentary (1080p video + photo), sound engineering (recently finish an award winning album) and occasionally into gaming.

I fist noticed the problem with the random shut downs like many of you. However, since the iMac went back to normal after a quick reboot I didn't think much of it. About 1 month or 2 ago I was playing a game on my iMac and the screen freaked out with green and grey lines. I restarted a few times and it was working again. Upon launching the game and playing for a few minutes, it crashed again -- this time without turning back on. I freaked out, tried PRAM reset, re-arranged RAM and had already stumbled upon this thread.

Confident apple premium reseller/supplier would fix this well known issue I took it in for repairs. The technician charged me IDR12,800,000.00 which amounts to around SGD1200 or around USD800 to replace the logic board. Completely ****** off at the late night email I received, I took it back without repairing it. To my surprise when I plugged it back in at home, it just turned on. I left the power chord at home, and I'm assuming this is the issue which many are experiencing = the longer you disconnect the iMac from the chord the longer it operates without shutdown.

I've used apple computers since the 3rd Gen iMac (purchased in 2001/2) and am completely disappointed Apple's service & care regarding this matter. I wish I was still in Singapore, perhaps the people there are more competent as compared to the "geniuses" in Jakarta (trust me South East Asia region can be a ***** to get repairs on any tech device). I had the original warranty for a year, and then purchased a 2 year warranty Apple Care which gave me a total of 3 years. Just my luck to be out of warranty, I would have much more of a bargaining chip.

My dilemma now is should fly to Singapore with my iMac and try my luck there with the more competent people, or sell this expensive faulty manufactured defect here in Jakarta after it's been shut off for a few days (so it has the appearance that it works fine) for around SGD 1600 or USD1100 (I purchased it originally for SGD3300 or USD2200).

Or should I try the Liteon replacement of the Delta PSU as the last few posts suggested. Please update us on this method... if it actually solves the issue. At this point I'm close to punching a hole through my iMac. I have clients waiting on their wedding album and like any professional it's embarrassing and bad branding to keep your clients waiting (I'm talking to you apple).

Thanks for everyone who posted on this thread, I thought I should add my experience too.

i have orderer a LiteOn PSU, i will keep in touch this case here and will say my results..

Same problem with my 2012 27" iMac

Been monitoring this ever increasing thread for a long time. Had my Imac into accredited Apple repairers who wanted to change back casing (god knows why) video board and logic board. Cost 950 euros and no guarantee to cure problem. Seeing what other have done, decided to bite the bullet and purchased a Liteon PSU. With great trepidation, stripped down the IMac,(following Ifixit instructions) and installed the PSU. It started straight away, I have updated all my programs (including Sierra). It, been running consistently now for few days but time will tell if problem is overcome. Won't say the installation was easy but with time, patience and continued referral to the instructions it was completed in about two hours. Go for it. I realise I have now invalidated my chances of taking part in any eventual recall, but I was left sitting with a expensive, useless piece of junk, so nothing lost. Have to say this is my fourth IMac and I was a Apple fan. The design and software are tremendous but all of my units have failed for one reason or another. I will never buy another Apple product. Have reverted to Windows 10 building my own units based on barebones NUC's linked to 32 inch TV monitors. Much cheaper, just as efficient and easy to repair/tweak.

Hello, did you changed the logic board and gpu anyway?.. or you just took the option to change the PSU only?

Many users over the net say that this is because a fault on Delta PSU coming from default on various imacs..

i have ordered my LiteOn PSU, please, keep in touch your progress with it... According to the shutdown behaviour, this MUST to be a PSU thing, since you must to wait at least 15 minutes without power cord connected to power up again, they are a PSU sympthom only.