2015 iMac 27" Retina Powering Off Randomly

Hi,

I'm hoping someone can help.

Lately my iMac has been turning off randomly and the only way to power it back up is doing a hard reboot.

Anyone know why this is happening? or how I can better diagnose the issue?

I ran the Apple Hardware Test several times and the report shows no hardware failures.

My experience is that when this sort of thing happens (and I've seen it a whole bunch of times), it has never had anything to do with software. It always has had something to do with either the Mac's power supply, or the power coming from your wall outlet.

In a few cases it was due to either a bad (or improperly adjusted - back when it was possible to adjust them) power supply, or one that had cold solder joints that needed to be attended to (just touching each joint with the tip of a soldering pen to reflow the solder was enough to fix things up).

But much more commonly it was due to something on the same electrical circuit that had too much of a draw, causing a sag in the power, and that sag caused the Mac (or Macs) in question to shut down. (Fortunately with no other obvious damage.)

Often the problem is that the user has a new laser printer. They have a huge draw as they start a new print job.

In one case the problem was that an office had a refrigerator in the break room, and when it cycled on it caused all (or most) of the Macs to shut down. (That problem perplexed the entire office, and it was fun tracking it down.)

In each of the latter cases the solution was to attach each Macintosh (but *never* a printer or the like) to a UPS that included automatic voltage regulation (AVR). (A cheap UPS that doesn't have AVR won't help!) This is the brand and model of UPS that I most often recommend:

CyberPower 1000AVR ($110 with free shipping)
http://www.amazon.com/dp/B000QZ3UG0/?tag=macforums0e4-20
or
http://is.gd/iaxI4

Randy, thanks for the suggestion.

I also have been looking around other forums and some iMac users suggest my problem is related to the logic board.

I also found this video on YouTube of a user who shows the same problem I'm having.

http://m.youtube.com/watch?v=P6RmhCeelDM

Besides all Randys advice I had 2 20" iMacs (the newer aluminum ones) that did just that. just shut off in the middle of things. Resetting the PMU fixed it in both cases. My power was fine.

dtravis7 said:

Besides all Randys advice I had 2 20" iMacs (the newer aluminum ones) that did just that. just shut off in the middle of things. Resetting the PMU fixed it in both cases. My power was fine.

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Resetting the SMC is certainly a good idea:
https://support.apple.com/en-us/HT201295

However, I would have expected that it would have already been tried as the only way to get the iMac in question to re-boot.

Thanks for the advice guys. I've had this happen once or twice with my iMac. In my case it has happened overnight while I was asleep so I am not sure whether the cause is a power sag such as Randy suggests (hadn't thought of that) or something else. At the moment I can't think of anything on the same circuit that would have that kind of draw though. It might also be a general power sag as we have had a few of those lately.

It hasn't happened often enough at the moment for me to really troubleshoot matters though.

I vote both. In the past here, we had a lot of electrical problems (come home, all clocks flashing). Once bad enough an old iMac was just nuked. Now the clocks no longer flash, and my brother bought me a big UPS.

However, I have also had that going on and the logic board was bad. Find a good shop for those repairs-this MacBook Air I'm typing on was quoted as $750 at the Apple Store. I said "nah!!!!" and got a new one for less than that via a friend who works at Apple. I then took this one to Adam's Apple and PC in Burbank where I've gone for years. $300 later, I had an extra MacBook Air

So I picked up a CyberPower UPS, but so far no luck ...

My iMac is still experiencing the same issue. I'm starting to feel like my problem is hardware related. I'm going to bring my iMac to an Apple repair shop this week.

markm186 said:

So I picked up a CyberPower UPS, but so far no luck ...

My iMac is still experiencing the same issue. I'm starting to feel like my problem is hardware related. I'm going to bring my iMac to an Apple repair shop this week.

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Make sure you have an appointment before taking it in. You don't want to lug a 27" iMac around too much. Also, be sure to tell the genius bar exactly what you've experienced with it powering off. They may just run some simple diagnostics and then tell you they found nothing wrong. A new iMac powering off like that could be due to an intermittent power supply, bad temperature sensor, flaky memory, bad hard drive, or a bad logic board. Let us know how it turns out.

Any chance it is still under warranty being a 015 model? If so consider taking out AppleCare before warranty expires for another two years warranty

Sadly my iMac started acting up a month after the Apple 1 year warranty expired... BUT ... I just found out that since I used my VISA cc to purchase the iMac, they offer additional coverage after the manufacturers warranty expires.

Here are the details: https://usa.visa.com/support/consumer/card-benefits.html

Also, an update on my iMac. So I left it unplugged for several days and just started using it again yesterday, and guess what?? it's no longer randomly powering off. Not sure what the problem was originally, but I'm glad it's working again. I also installed iStat to keep an eye on the internal temperatures.

Thanks for that reminder. That's always a good thing to check. Most of the major credit card companies here in the US have a similar policy but it may or may not apply if you use your debit card.

Also, an update on my iMac. So I left it unplugged for several days and just started using it again yesterday, and guess what?? it's no longer randomly powering off. Not sure what the problem was originally, but I'm glad it's working again. I also installed iStat to keep an eye on the internal temperatures.

Click to expand...

By doing that, you basically did a SMC Reset!!! A good choice to use with a goofy acting Mac. Call it a full shutdown/reboot but on Steroids…
https://support.apple.com/en-us/HT201295

Most of the major credit card companies here in the US have a similar policy but it may or may not apply if you use your debit card.

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It doesn't apply for debit cards as it's assumed the funds are available and debited rather than a payment plan with interest. Always good to keep a credit card like Visa or Mastercard along with your debit cards. I never pay using a debit card when making a large purchase. The debit card is for grocery shopping. ;D

The debit card is for grocery shopping.

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Hmmm…??? Sounds like another Costco shopper… also my wife's favorite store I think…

I used to have a business membership to Costco but let it expire. I'm not really keen on paying $50.00/year membership fees when there are other stores that are competitive with Costco or Sam's Club. Besides, being a retired military member I have access to the Naval Base stores in Fort Worth. No state tax and usually a good savings on all items.

I DID mention the SMC reset above but most did not feel that would do it. When my iMacs did this very thing it worked every time.

dtravis7 said:

I DID mention the SMC reset above but most did not feel that would do it. When my iMacs did this very thing it worked every time.

Click to expand...

It never hurts to try it IMHO, especially when nothing else has worked, and it's been a basic standard Mac fix for years, even if the name and procedure might have changed over the years. And good advice I'd say.