Level 1

9 points

iMac shuts down randomly for no apparent reason

In late August of this year, after the plug came out of the back of my iMac when I was attempting to adjust the angle of the screen while the computer was on, the computer began shutting off for no reason while on. I took the iMac to the Apple Store in El Paseo, in Palm Desert. They replaced the 3 TB fusion hard drive saying that there had been a history of problems with this. I received the iMac back and shortly thereafter began to shut down once again for no reason. I brought it back to the Apple Store and they deleted some software and removed some software that were automatically engaging at startup. The iMac began to shut down for no reason once again. I brought it back in and they ran a full diagnostic test and could not find any problems. It worked for a while and then began to shut down for no reason again. I brought it back in to the Apple Store in this time I was advised that there are going to run more extensive hardware testing, running it through longer cycles etc. They could not find the problem and suggested that it was likely an effect of peripherals I had connected to the iMac. I disconnected all the peripherals from the iMac and began testing them one by one over time. The iMac still shut down for no reason at random times. I ran the computer with no peripherals connected at all, and it still shut down for no reason. I have run Apple diagnostics and it found no trouble. I have run malware detection software and it found some things that were then deleted. I did this very early before I even brought to the Apple Store. I ran antivirus scans, full scans on the iMac and it found no infection. I also ran fan control software to see if the iMac was overheating and even with the fans at the full rpm setting, the iMac still shut down at random times. I used a rocket air blower that I used to remove dust from my camera lens to try to blow through the back vent and the bottom screen vents to free that of any buildup of dust, and it still shut down for no reason. What could possibly be the issue with this machine after all the testing and interventions that have been done?

Late 2012 iMac - Quad Core Core i7- 16GB, 3TB Fusion Drive

iMac, OS X Yosemite (10.10.4), Mac (27-inch, Late 2012) 3.4 GHz

Posted on Nov 3, 2015 3:50 PM

87 replies

John Galt

Level 10

155,282 points

Nov 6, 2015 8:04 PM in response to mikestan56

I recommend you bring it back to them and tell them it's not fixed yet. Whether to replace the logic board, power supply, or both is a question of who's paying the bill.

The problem you describe is identical to, and indistinguishable from, a power interruption. That power interruption can be internal to your Mac or external to it. That's all anyone knows. I described the potential causes, and they are not limited to the power supply or the logic board. It would be unfortunate to replace one or the other just to find that your building power is unreliable. You could eliminate that possibility by using a UPS from a reputable manufacturer.

westom

Level 1

4 points

Nov 6, 2015 8:29 PM in response to John Galt

Building power is obvious by monitoring an incandescent bulb powered from the same receptacle. A bulb can dim to 40% intensity. Even that is sufficient power for any computer. If bulb is not dimming, then building power is more than just fine. Move on to other suspects.

mikestan56 Author

Level 1

9 points

Nov 13, 2015 8:12 AM in response to westom

I just purchased a new APC 750 backup battery/surge protection system with UPS. I tested the computer right away and it still shut down for no reason. I got online with AppleCare technicians on chat and we ended up wiping the hard drive, rebuilding the fusion hard drives, and then the plan was to reinstall the system. The technician directed me to work in terminal and the process to rebuild the drives got hung up. I'm taking it in tonight to the geniuses at the Apple Store once again. Now, my iMac is unusable until the drives are rebuilt and then they can possibly see what the real issue is. That was the last thing they are going to do before determining that it was in fact a hardware issue. The hardware issue has not yet turned up on any of the Apple diagnostics or the hardware stress analysis that the geniuses went through on two occasions with my iMac before. It may well end up to be a logic board problem, which will be very expensive I'm sure.

mikestan56 Author

Level 1

9 points

Nov 13, 2015 8:17 AM in response to John Galt

At this point, I am of the mind of having them keep the iMac until it is completely repaired. It has been a nightmare and very atypical in all my years of using Mac computers. Couple of nights ago I was on chat for almost 4 hours with the tech going to the process of wiping the hard drive and trying to rebuild to drive. Now the Mac hard drive is not even available to restore the system or reinstall a new OS X. Hopefully they can figure it out and get it right this time, it may end up costing me a bundle-which is frustrating because I paid $2800 two years ago to buy the iMac in hopes that it would be reliable for many years.

John Galt

Level 10

155,282 points

Nov 13, 2015 8:37 AM in response to mikestan56

I'm sorry to tell you but as I have repeatedly stated the problem has nothing to do with the hard disk drive or its contents. system.log is repeatedly recording a sudden interruption of power, which can occur for a variety of reasons. If you ruled out external causes, the only remaining ones are #5 and 6 above. Everything else is a waste of time.

At this point, I am of the mind of having them keep the iMac until it is completely repaired.

I agree. If they are at a loss then suggest they replace the iMac's power supply. It is one of the least expensive components to replace.

westom

Level 1

4 points

Nov 13, 2015 8:39 AM in response to mikestan56

Find yourself a tech with basic computer knowledge. Power off and power on is controlled by a piece of hardware called the power controller. It even monitors a front panel power button to decide when to power cycle a machine. Once power is on AND after a power controller decides everything is OK, then it decided to let the CPU execute.

Nothing on a hard drive in involved. Only technically uneducated techs would 'shotgun' - fixing things on wild speculation. An informed tech would have used a meter (that even a 13 year old can use) to see a defect long before fixing or changing anything.

Software is not permitted to operate until a power controller finally decides hardware is stable - then let the CPU execute. An informed tech would know that. Uninformed will shotgun - replace things (or software) only on wild speculation.

Did you ignore what an engineer said? First indication of an informed recommendation. It says not change anything. First collect facts. Changing comes much later when facts define a suspect. Why waste money on a UPS? Since all computers must be perfectly happy even when the bulb dims to 40% intensity. That UPS was another classic example of shotgunning.

A TV show taught how to solve all problems (not just computers). Follow the evidence. Amazing how many never understand or do that. What was done demonstrates how not to solve problems.

mikestan56 Author

Level 1

9 points

Nov 13, 2015 12:41 PM in response to John Galt

I have copied and printed your post along with Westom's, to take with me to the genius bar tonight. I really appreciate your assessment of all this. Man, they need some real tech experts who know what they are doing there, unbelievable...

mikestan56 Author

Level 1

9 points

Nov 13, 2015 12:43 PM in response to westom

Thank you very much. I am taking your posts with me tonight to my genius bar appointment. I will tell them to fix what is wrong and that I want my iMac back with confidence that that is my last trip to them for this problem...

mikestan56 Author

Level 1

9 points

Nov 21, 2015 6:37 PM in response to John Galt

I took it back to the Apple Store. They had it for a week. They said they ran comprehensive tests on it and could not reproduce the problem. They said it was likely my third party fan control software that was interfering with the built in fan, causing the fan to not work properly - making the iMac overheat and then shut down. I deleted all the third party fan control software: SMC Fan Control, Mac Fan Control. I only had my external super drive, printer, and USP back up battery device plugged into the iMac USB ports. I was running the machine for an hour running: GIMP, Photoshop Elements, iTunes, and Google Chrome Browser. I was ripping a CD and working on digital photo images when it shut down again. It would not start by pressing the power button. I reset the SMC, waited 30 seconds, plugged it back in, and then waited five seconds and then pressed the power button. It started booting, came to the desktop screen and then shutdown again. I repeated the smc reset and it it booted back up and now has been on for a few minutes. I am thoroughly frustrated with the Apple techs and support service - it seems as though they don't know what they are doing. I told them what you suggested as the problem, and I don't think they even considered that. I have now taken it in five times. I am ready to trade it in on a used Powermac...

mikestan56 Author

Level 1

9 points

Nov 21, 2015 6:38 PM in response to John Galt

took it back to the Apple Store. They had it for a week. They said they ran comprehensive tests on it and could not reproduce the problem. They said it was likely my third party fan control software that was interfering with the built in fan, causing the fan to not work properly - making the iMac overheat and then shut down. I deleted all the third party fan control software: SMC Fan Control, Mac Fan Control. I only had my external super drive, printer, and USP back up battery device plugged into the iMac USB ports. I was running the machine for an hour running: GIMP, Photoshop Elements, iTunes, and Google Chrome Browser. I was ripping a CD and working on digital photo images when it shut down again. It would not start by pressing the power button. I reset the SMC, waited 30 seconds, plugged it back in, and then waited five seconds and then pressed the power button. It started booting, came to the desktop screen and then shutdown again. I repeated the smc reset and it it booted back up and now has been on for a few minutes. I am thoroughly frustrated with the Apple techs and support service - it seems as though they don't know what they are doing. I told them what you suggested as the problem, and I don't think they even considered that. I have now taken it in five times. I am ready to trade it in on a used Powermac...

babowa

Level 9

78,562 points

Nov 21, 2015 7:14 PM in response to John Galt

Sorry for adding a question here; out of curiosity, what would be the most likely problem if the shutdown cause had been the number 5 (in addition to some 0's)?

I just started to experience several strange behavioral problems and will be addressing it with Apple (and I have Applecare) as it shuts down with or without an external drive attached, and after doing an NVRAM and SMC, whether it is plugged into the UPS or the wall. I'm using the weekend to make sure all my clones are updated, etc.

Thanks for any insight.

mikestan56 Author

Level 1

9 points

Nov 21, 2015 7:20 PM in response to morrispe

I was dumb and did not extend my warranty to 3 years. I just had faith in the machines until this. They may not be able to help me. I may just trade it in on a used Power Mac through Power Max, since they cannot reproduce the problem in their shop. If it was a logic board then I'd really be screwed...

babowa

Level 9

78,562 points

Nov 21, 2015 7:26 PM in response to mikestan56

Ahh, that is unfortunate - I've had Applecare replace 2 logic boards, a hard drive, a Superdrive on various iMacs and got a new Macbook Pro last year after they could not figure out what was wrong with my old Macbook (that was one week before Applecare expired). In my case, purchasing Applecare paid for itself and more as logic board replacements are rather pricey. I'm gathering enough info so my call to Apple will hopefully be somewhat easy...... FWIW, mine is a late 2012 3.4 GHz refurb machine from the Apple store - mine has a regular hard drive as I do not want a fusion drive.

John Galt

Level 10

155,282 points

Nov 21, 2015 8:34 PM in response to babowa

babowa wrote:

... what would be the most likely problem if the shutdown cause had been the number 5 (in addition to some 0's)?

For desktop Macs, 5 indicates a normal shutdown initiated by either Restart or Shut Down menu selections, so you would expect to see that most often. Portables might be different, perhaps 3. I'm relying upon memory.

0 is a power loss. That can occur for anything other than an orderly shutdown, such as any of the six examples I posted. Since a power loss is not initiated by any controlled event that's all the system can determine.

babowa

Level 9

78,562 points

Nov 21, 2015 9:05 PM in response to John Galt

Thanks for that - the strange thing is that there were no normal shutdowns (that I'm aware of) except my using the power button when it was already completely non-responsive/black screen/seemingly dead.

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iMac shuts down randomly for no apparent reason