iMac randomly restarts

Hello everyone, I noticed that everyone here had a 2.4GHz machine but I have a 2.8GHz that is also having random restarts and freezes. Here is my story and my thoughts on the issue. I've had my Mac since November 07 and have not had any issues since. I never turn my Mac off unless I go away for a few days, so at night I always put it to sleep. About a week ago when I came back to my Mac after work I noticed that it was shut down. At first I didn't make anything out of it but when it happened several times I knew something was wrong. So at first I figured, well my issue here is that it is shutting down instead of sleeping. But now I get several random issues.
1. The Mac will chime and boot, but I will get no video (have to force shut down unit)
2. The Mac will chime and boot but will freeze soon after (keyboard and mouse unresponsive)(another force shut down)
3. The Mac out of the blue will just restart.

When the issues started I disconnected all external hardware just leaving the kyb and mouse. I have reset the PRAM and Power Manager. I have performed an extended AHT (Apple Hardware Test) with no errors and no problems are found on my Hard Drive.
I turned to the Console app to try to make something out of what was going on.
I noticed quite a few errors and I'm still in the trial and error phase to see if some piece of software could be at fault. I do have my mac in a UPS, and I haven't ruled that out as a possibility, but I doubt that is the problem. I don't think it is software or UPS related, as the freezing and rebooting occurs at different stages of the booting process.
I have also re-installed the full 10.5.2 combo update but that has not resolved my issue.
I don't suspect over-heating as the issues have occurred when the machine had just started.
This is becoming a serious issue as it is definitely not good for the hard drive and of course it is counter-productive.
I am going to do some more troubleshooting over the weekend but if the issue is not resolved after that I will call AppleCare.
Every Aluminum iMac should still be under warranty so take it to Apple if necessary, but don't forget to back up your data if you can still access it.

responding to wickhama, the operating temperature that you mention (50° to 95° F ) is not the operating temperature of your Mac, it is the recommended operating temperature of the location where your mac is.

I also heard the mention of the software smcfancontrol. If that works for you that's great, but you shouldn't need to do that especially if your iMac is still under warranty.

Good luck to everyone and I'll try to keep you posted on my progress. So far I've had it running fine for about 2 hours. We'll see tomorrow when I wake it up!

I brought the machine back to the Apple Store and they went ahead and offered to replace the power supply for me since it's still under warranty. It took a few days because they had to order the part, but I just got the iMac back and it hasn't restarted yet. We'll see how it is performing tomorrow.

Jason

The next day the random restarts continued. I tried logging in to a new account I had created in the past for my wife, but the unit still restarted and froze.
One thing I did notice is that it did not restart or freeze at all while playing Warcraft 3, which is graphic intensive, which wouldn't make the graphic card the culprit.
I'm burning some DVD backups before I bring it or send it to Apple. I will do one more test with a new install of 10.5.0 but I need to find an external drive free first 🙂 If no freezes or restarts occur with a new system, then we will know it is a software issue and not a hardware issue.

Does everyone here who has the issue running 10.5.2 or an earlier version?

I bought a refurbished iMac 2.0Ghz about a month ago and within a couple weeks it developed this random restart issue. I'm running 10.5.2 with only a HP C4280 printer, keyboard, and ethernet attached. Basically, it's still out-of-the-box with just a few 3rd party apps - Firefox, etc.. I do have a Belkin surge protector in use, but have used that for years on my G3 with no issues.

I called Apple support and they said that this problem is common enough that it is being investigated by Apple Engineering. After asking a lot of questions about my system and how and when the problem occurs, they said to take it down to the Apple Store to test for hardware issues.

I have also noticed that my fan runs at 3500rpm ALWAYS, idle or used. But the chip temp is only 100F max, and mostly around 85-90. Temp seems unrelated to the restart.

Went to the Genius Bar and they said to reinstall the OS.

Mine started randomly rebooting a few days ago and Apple support advised me to re-install the OS when I called them, but I didn't do so. Mine restarted randomly regardless of how it was booted, either in OS X, Windows Vista or from the OS X installation DVD, and the problem increased in frequency the longer the iMac remained on.

I would say it's almost certainly a hardware problem, perhaps the SMC chip, so re-installing the OS would be a significant waste of time. It is currently at the Apple repair center where I expect they will be replacing the motherboard.

Just something to add to the discussion.

We have a brand new 1.83GHz C2D Mac Mini with OS X 10.5.2 and 1GB factory RAM installed on it. It's restarted itself a half dozen times in the last two weeks. "Restart automatically after power failure" is not active. Today, it just shut down - no restart.

We also have a 17 month old 2GHz C2D iMac with OS X 10.5.2 and 2GB Apple-installed RAM installed on it. Since I upgraded to OS 10.5, this one has restarted itself twice. "Restart automatically after power failure" is active. Unfortunately, it's too old for Warranty service. The only other concern I have is that I don't believe the iMac did a full restart - I think the screen just went blue and then the Finder reappeared and everything that starts up automatically on boot did so.

Beyond being on the same network and using some of the same app's, the only thing these two machines have in common is OS X 10.5.2. _I believe OS X 10.5 has something to do with it_ because it didn't start happening on the iMac until 10.5 was installed.

I have reinstalled the OS with the Combo Upgrade, as was suggested somewhere, and I will delete the com.apple.autowake.plist, com.apple.powermanagement.plist & com.apple.systemuiserver.plist files as was suggested in another discussion. I don't believe the RAM is an issue as it's all factory installed on both Mac's.

In contrast, we have a 1.83GHz iMac running OS X 10.4.11 and a 2.4GHz MacBook Pro running 10.5.2 and neither of them have experienced random restarts.

I'll try to watch both afflicted machines more closely (and check Console) to see exactly what is happening and if any "fixes" work.

I called Applecare to let them know at least what was going on and to get a case number on file. They advised me to take it in to an Apple Store but I told them that I wanted to try booting from 10.4 or a clean 10.5 first. (And also do more backups)
I haven't had time to do that yet and my machine worked without issue for a week then once when I woke it from sleep it just froze. Did a hard shut down and it has been working ok. It is a very strange issue that is hard to pinpoint.

I have a non-aluminum Core Duo 2GHz imac at work with 10.5.2, and have not encountered any of these issues.

Strange, very strange.

After seeing my repair status reported as "On Hold - Part on Order" for the past three days, I called AppleCare and was told that it would be at least another week before they get a replacement power supply (the identified cause of the random restarting problem) for my dysfunctional iMac. You'd think they'd keep a sufficient supply on hand!

I use my iMac for my work, so this is not a small problem. Perhaps the naysayers are correct, after all, in that professional users have taken a back seat to the consumer market. Such slow repair service is entirely unacceptable.

Well, I was hoping that the new iMac Firmware update would fix the issue but it hasn't. Today as I woke my iMac from sleep I got a black screen and no response from my keyboard or mouse. Had to force shut-down.
I still need to boot from an external in 10.4 to see if that resolves the problem but I was hoping not to have to try that. Maybe the 10.5.3 update, when it comes out, will fix this issue. sigh

The random shutdown/reboot problem is caused by a bad power supply. You will need to have your iMac repaired or replaced.

Hello Capaho, can you elaborate on this? Have you had a similar experience and had the Power supply replaced and everything worked again? In all my years of being an Apple user and tech I have never seen a unit act like this.

I just tested the unit with original Apple Ram for a few days and there still are issues, so I've ruled out it being a RAM problem. Last test I want to try is booting from 10.4. If I still have issues with 10.4 then I can confirm a hardware issue and it will have to take a little "vacation" to the Apple Store.

Thanks

regards

Hi Yanik,
I bought a 24" iMac for my wife this past Christmas. I loaded it with all it could take so that I wouldn't have any problems with memory or processor upgrades later (that happen to me with an older PC) so i decided to switch to Apple and spend money now to avoid headaches later. Well, all was fine for all this time until about two weeks ago when my wife was working on a research project for school.At the same time she was uploading some pictures on the web and she tried to start itunes for some background music. Well the mac restarted all by itself but at the time my wife didn't think much of it. she thought it was an automatic update (even though she had rejected to do the update at the moment it let her know that it was available). The computer worked well for the next 1 1/2 until it shut down completely. After talking to Apple tech support, going thru all the troubleshooting procedures they finally told me that I needed to take it to an Apple Store. Eventhough the nearest Apple Store or authorized repair shop is 300 miles away I took it and after a week now "it seems" (crossing my fingers) that it will be ready to pick up this weekend. When I called the 800 number to Apple tech support to see what the problem was, all they told me was that the store had ordered a power supply and a main logic board. I never had any problems before this and i am hoping that this will be the end of it...or else I don't know how I will convince my wife that Apple REALLY is superior to any other system, she was VERY doughtful before all this. Now I'm just in damage control mode. I'll let you know what happens when I pick it up later this weekend.

Adam

Has there been a clear answer to this? Has Apple responded and do any of you have solutions?

No fix yet! I have an early-2006 iMac (white 20") with Interl Duo, and to this date...it still has random restarts. In fact, I took it in two weeks ago, they replaced both the Power Supply and Logic Board, and the same night I got it back...it shut down, and continued to do that for the following week! I have since taken it back...they have performed some stress test on it and claim that they can't find the problem...and are asking "me" if I want them to continue testing or pick it up! If it doesn't work, why would I want it back! And generally, the cause is during non-use with the computer left on with a few application open, as opposed to physically using the computer!

Crazy..I have no idea what to do...and it sounds like Apple doesn't have a solution either, even though this seems like a common issue.

I can see the next Microsoft commercial...showing iMac's shutting down and PC's running strong...

Hello again,

I'm pleased to say that I have found the culprit to all the crashes/freezes my iMac has had. It was all due to one defective 3rd party RAM chip. Nothing else.
The reason why I didn't catch this at first is that my 2 RAM chips had passed the extended Apple Hardware Test.
So after some research I found this helpful ram utility which I ran in Single User Mode and BAM! it found a defective chip.
This utility is called Rember. (You can find it on versiontracker).

I returned the defective RAM module, received a replacement (which tested ok),and I have had no issues since.

Hope this helps some people. Give Rember a try and you'll know if RAM is the issue.

regards