Intel IMac Turns off spontaneously!
 

So,
My 2-year-old intel duo core IMac has recently started shutting down--well, actually turning off, spontaneously. I first noticed it a few months ago--just every once in awhile. It is connected to a UPS, but the battery for the UPS always says it is fully charged, so I don't think it's that the UPS needs a new battery. It is as if it is getting a signal that the electricity is shut off, except that if that is the case, the APS should kick on, and it doesn't. Within the last two weeks, it has begun shutting off approximately every 3 days. I've checked the system log, and it doesn't even say anything about it shutting off, so it's happening too fast to even log it! Temperature-wise, the lab I am in is about 65 degrees, and the computer is on a desk in the middle of the room, so it gets plenty of circulation. I'm pretty well convinced it's some kind of software problem, but I'm at a loss! I've done a system check to be sure there isn't any damage to the hard drive, and it does not find any.

Check your energy saver prefs
 

Any chance someone scheduled an automatic shut down using "Energy Saver" in your Sys Prefs?

Have you done all of the SMC firmware updates and EFI firmware updates available for that iMac?

Make sure to Zap the PRAM and Reset the SMC.

Trevor

I've checked that, and there is nothing scheduled. Under power adapter: I have "never" for put the computer asleep when it is inactive; and 2 hrs for putting the display asleep. Under UPS, I have it set to shutdown when it has been on UPS power for 10 min, shutdown when the time left on the UPS is 1min, and shutdown when the UPS power level drops to 1%. I have it set to put the computer & display asleep when it is inactive for 15 min. But, the strange thing is I really don't think it's any of these settings because I've had the UPS for about 2 years, and once the settings were set never changed them again, and it says the battery is at 100%.

I believe so, as long as they're all available under the "apple" & software updates. My colleague has the same computer and keeps it up-to-date also and does not have problems.

Check your connections o the UPS and the wall socket. If it's old wiring there could be a short somewhere that occasionally acts up.

Of course there is the possibility that someone is playing with the breaker.....every now and again.

It might be a good idea for you to specifically try to apply the SMC and EFI firmware updates available anyway. If they've already been applied, no harm will be done.

Also, you seem to have missed the second paragraph in my post above. Have you zapped the PRAM and reset the SMC? Links are given above with detailed directions for how to do each of those steps.

Trevor

The firmware updates have been applied. I just reset my SMC (well, per the instructions. Is there any way to see in some log or something that it was actually done?) We'll see if that helps, if not, I'll zap the PRAM. If it is on schedule, it should turn off today or tomorrow. Thanks for the info!

Maybe it should marry my MacBook which turns on randomly even when shut down not merely asleep in an empty room.

Then they could produce mid-sized Macs with proper awake and sleep cycling!

The first thing that I would've tried was to unplug the Mac from the UPS and plug it into something different, even just directly into a wall.
If the Mac maintains the same conditions, then it's the Mac. If not, at least then you know that there's something going on with your UPS.
Do the simple stuff first.

Is the UPS properly grounded? An APC will have a red LED labeled "Building Wiring Fault" that will come on if the ground is not connected. The battery will not kick in if there is no ground, so a sag will cause the computer to shut off.

And so it shut down again Thursday night--on day 3 again. I just zapped the PRAM. After I check to see if that works or not, I'll try just plugging it into the surge protector part of the APS instead of the special "shut down" part.

Anyone heard of a hardwired switch on an APS that sets a shutdown schedule?

It's odd, this computer has been plugged into this APS for over 2 years now, and another one used the same wall outlet, and both were bought brand new.

Alright, after zapping the PRAM we've made it all the way to Wednesday morning, way past the normal three day limit! That may have fixed the problem, I'll post an update when I'm fairly confident in the outcome.

Any luck? I am having the EXACT same problem with my wife's iMac (20" mid-2006) and am totally stumped as to what is causing this. I started getting this problem when I upgraded her computer from Tiger to Leopard 3 days ago. Now, it turns off every 40 mins or so.

Here is what I have done and the problem remains.

- Reinstalled a totally virgin OS X Leopard. Software is not the issue.

- Overheating seemed like the cause, but after installing iStat, there is nothing unusual about the temps - 48C for the CPU. I am sure that can go as high at 60-70C. All fans seem to be working.

- I believe that I have the newest firmware installed. Software updates indicate that I do. And, when I ran the installed apps for the firmware, it also indicated I was current.

- Reseting PRAM is not the issue. There isn't a clear way to do it on this model iMac (no buttons to push, just pull the power cord???). Anyway, the computer doesn't start up again until after at least 15 mins, so the PRAM gets reset anyway.

So what in the world could this be?????? Tomorrow, I am probably heading to the service center. Otherwise, my wife (that's her => :mad: x 100) is going to have my head for pushing her to upgrade to Leopard.

I hate to say this, but I suspect you may be having a power supply problem which will necessitate your contacting your Apple dealer. I had the exact same problem with my 2004 iMac. The first sign of trouble was when it shut down after I had put it to sleep and got progressively worse until I only had to leave it for 10 or 15 minutes to come back and find it switched off. As this was a known issue and even though my guarantee had long expired, I was given a free repair. However, I am surprised that your Core Duo machine is experiencing this problem after only two years.

(Not so) Perplexed

Well, you've tried everything I've tried, except that I reset the SMC as well as zapped the PRAM, and mine seems to be ok. I haven't run into the problem again. I agree that it's not an overheating issue, I look at that as well and your computer is running well below what mine was. Sorry I can't be of more help!

Well, against my desires of being placed in the hands of a $-happy technician, I broke down and delivered my iMac to an authorized repair center on Friday. Should find out something by next week. I'll report again..

No, pulling the power cord does not zap the PRAM, nor does leaving it off and unplugged at least 15 minutes. Those things do nothing except wear down your PRAM battery.

You zap the PRAM of the Intel iMac the same way you zap the PRAM of every Mac, you turn it on and immediately hold down Command-Option-P-R. Keep those keys held down until you've heard the startup chime 3 or 4 times, then let them up.

Trevor

Log files
 

Look in the system.log file for "Previous Shutdown Cause". If it's 0, 3 or 5 then it's normal. If it's a high number like -110 or -122 then it's a hardware problem.

My mistake. Meant to say the system management controller (SMC).

UPDATE: Got the call today from the service center and was told that my power supply was defective....

So, I have not had a problem with this since resetting the PRAM. It looks like that was the issue for this particular instance. My advisor is having the same problem, but it is much more frequent than mine was--up to like every 15 mins or so. I gave her the instructions on how to reset the PRAM, I'll let you know if it works. I'm going to guess that hers is a power supply problem. Oh, and it's not an intel mac, its the version right before it.

A bit late to the discussion, but need similar help
 

I realize this topic was back in 2008, but I am having the same problem today. I have a 20" Intel duo 2 iMac that has spontaneouly shut off twice. At least I thought it had. WHen it happened today I put my hands on the machine and my ear against it and it was not off. Just the screen was black. It was like it had actually gone to sleep, but could not be woken up. I finally just held the power button twice until it restarted. Then I came here to check the problem out. I looked in the system log as suggested (had to google how to do that) and discovered something very weird. I have an application called Alarm Clock that I use every day to wake me up. It's set for weekday wake-ups and a Sunday wake-up. Well, the system log had this report from the moment the screen went black:

6/5/11 11:32:13 AM Alarm Clock[1709] kIOMessageSystemWillSleep

6/5/11 11:32:13 AM [0x0-0x93093].com.digitallity.alarmclock2[1709] 2011-06-05 11:32:13.378 helper[9648:903] Adding power event: 2011-06-07 06:25:00 -0500

What's weird is that it says an event is scheduled for 6:25 on June 7, which it is, but that is a Tuesday. There is the exact same event scheduled for Monday June 6 that isn't mentioned. Somehow, it seems that Alarm Clock looked at the upcoming Tuesday event and then put the computer to sleep - so deeply it wouldn't wake up.
Is that what it looks like to you guys? Should I uninstall Alarm Clock?