Q: Why is my imac shutting down by itself?

last night i did use the red light switch of the socket and this morning i had 2 shut downs so maybe it's wiser to completely take the imac power plug from the socket to avoid any contact with the 'outside world'

I'm using a multiple socket expansion though mine is one a bit more secure, maybe there's a difference. But for testing it, perhaps its best if you disconnect from the wall then. Let us know what happens

Diogo,

     In my experience this is not a solution. Here in my office we always connect all systems (6 computers, 4 macs, 2 windows) to a UPS and the UPS will regularly shut down at night. Recently I pull the power cable of this Imac for last 2 months. It doesn't make any changes. I can't get it to work for more than two hours. During weekend the Imac is isolated from power outlet for 2 days, again on monday morning it will shutdown before 12pm, hardly I get 2 hours. Yours may be in an initial stage, but I assume this will change gradually.

     My study over the internet reveals only a few Imacs recovered by replacing power supply and or logic board. Most of the users would have abandoned their systems and may have found alternate arrangements. In my case I am now fear full of buying another Imac. Just google "Imac 2015 shutting down unexpectedly". Again I don't have the money to buy a MacPro.

Rajiv

Rajiv, this might be effective in cases like mine, but depending on the machine and the condition, other measures might be needed (things I was avoiding, such as replacing certain parts of the iMac). Several days ago I was really frustrated and ready to take my machine to the apple service. I did all I could do at home to try and locate the issue (all the known steps). Nothing worked. It wasn't the Ram either. I started to do this method and now it's working. I know this is not a permanent solution and I will need to go to Apple nevertheless. My concern is that my machine went out of warranty in March 2015. Though this is not my fault, I'm sure Apple will charge me. This method is just buying me some time until I have the patience to go through the process. Until then, I'm not having random shutdowns...

As I stated in previous comments, unplugging from the socket is what I've been doing since December. It definitely helps though if you keep it connected too much time, shutdowns come back.

found lots of posts about installed ram that could be the culprit; samsung and corsair are (reportedly) better than crucial; are they right?

the manufacturer of my 16 gb ram is 0x80AD which seems to be original apple ram but apple does not manufacture ram so i am not sure who is the manufacturer;

my last shutdowns showed a -128 error in the console, not very clear what the cause is but people with the same error discuss the ram issue:

http://forums.macrumors.com/threads/27-random-shutdown-previous-shutdown-cause-1 28.1184111/

took the power plug out of the imac last night, this morning i had a shutdown after 2 hours of operation;

in this case i was simply browsing the internet, nothing special, when it happened;

shutdown code: -128

i found a forensic report on the internet, that also listed the shutdown codes, it said: -128 Unknown

i am not sure if i'd rather have the code 0 (power) or the -128

CEIZ, I am curiously watching the console log and I am getting error code similar to this. Shutdown Cause: 0

Is it a indication my Power Supply is faulty.

rajiv,

i'm glad to inform you that it seems that i have nailed down the problem; spent many hours on the internet, going from forum to forum until i found the place where, in al thread of more than 400 answers, a lot of interesting info showed up; of course i can not be sure that my solution also works for you but you might take a closer look and test it!

in short: i have a mid-2010 27 inch imac with 16 gb of ram (hynix); the imac and this 16 gb ram do not work together nicely, causing the sudden shutdowns; if you lower the ram to 12 of 8 gb the problem is solved; i took out 2 modules of 4 gb and now the imac has no shutdowns anymore while before i experienced shutdowns twice a day; although my imac works fine with 8 gb ram i just ordered 2x2 gb to bring it to 12 gb again; important is that these  modules has to be from apple/samsung because they work fine together with the other 2 4 gb modules; so in my case there is no heating problem (i turned off the Mac Fans app without a problem); i was shocked to read in all these posts how many people had their power unit and logic board replaced, after an advice from the aple technician, to find out that these replacements did not solve the problem; if you are interested to read that thread yourself i can look it up for you and post it here; by the way, my ram was from hynix, as mentioned, but this does not mean that the problem only appears with this brand, a lot of 'victims' had crucel installed in their imac;

hope this might be helpful for you!

one other thing i should mention: the shutdown cause i got was -128 (known as 'unknown') while yours is 0 (known as 'Battery Removal/Power Plug')

CEIZ,

This RAM thing was tested in the very early state of this symptom and didn't help.  But didn't tried with 8 GB. I tested with 12 GB by rotational replacement of all 4 module installed just to isolate if a RAM stick was defective. Now reading your post I just took 2 4GB sticks away and while typing this only with 8GB (2x4). And it is installed by apple original Vendor name (code) is 0x8AD. I am not hopeful on this, just a try. As I am always getting Error code 0 may be replacing the PSU may work. But at the cost of some $$$. Not a sure spending. Just checking luck. My system is late 2012 -27 inch - i7 - 16 GB.

Rajiv

since your machine is a different one and the issue i am talking about seems isolated to the 2010 machines plus the fact that we experience different shutdown codes i fear that the ram solution may not work for you; however, somewhere out there, on the internet, there might be a forum/thread that addresses your specific problem; however: it takes so much time to check out all this sources... :-(

My iMac is late 2012 version. I've a question about if it can solved by changing from the original drive to SSD...whether it is possible.

Bella Joey, Don't think so. In my experience I demolished the built in fusion drive and Mavericks installed in the built in Intel SSD. My system is still shutting down. I am hopeless now. Had a call with Apple care India yesterday. The guy asked me to do certain basic tests such SMC, PRAM AHD and to delete system/library/configuration playlist files. Did all thing again. Just half hour later my system again shut down on its own. I am hope less now. The next step is to take my Imac to Apple service. I have no warrenty. So it is $$$$.

Rajiv

i have no idea if this will help you,

are you experiencing the same shutdowns as described in this thread? i guess so;

i hope you have read all the posts i this thread, it takes some time but it will give a nice overview of all the possible causes of the shutdowns, and the possible solutions; since you have a 2012 machine i would also do a series of additional google searches with the words shutdown imac 2012 and so forth, it might lead to other threads where your 2012 machine is discussed; as said, it will take some time but it might bring you to very helpful discussions

rajiv,

not to discourage you, but there have been people bringing their imac to apple and picking it up 'repaired' to discover nothing had changed and the shutdowns were still there; but i guess you have a guarantee on the repair service so you could bring back the machine to them until it is solved, or they offer you a new one