My iMac keeps turning off

It sounds as if your computer is overheating, vacuum the vents. If that doesn't help, it may be your power supply unit. Look in Applications>Utilities>Console for any notes in your system log about maximum temperatures being exceeded for longer than 30 seconds. That will be a definitive sign of thermal problems.

You can also try to reset your SMU.

Let us know how you make out,

There seems to be a contradiction in the listing of your computer, there is no such thing as a G5 intel, you either have a G5 PPC or an intel. In either case (and please clarify) try resetting the PRAM and see if that does anything. If not, try the SMU reset again.

Hi Jaijo: In addition to Miriam's advice, you may want to check for rogue processes running. Go to Applications > Utilities > Activity Monitor, With Activity monitor running check on the CPU column to sort and select All Processes in the drop down box. Is there some process or application using a high amount of the CPU? Print-job seems to be a popular one..

Stedman

Yes, reset the PRAM.

I would think that if you are having a thermal issue, the fans will cool things off and prevent a forced shutdown. The best thing would be to take it in or to call Apple and see what they suggest.

I have had the same problem with my 20" iMAC G5 for about two weeks. The random shutdowns do not appear to be associated with any particular software-ie during DVD play, email, internet with Safari. My apple care warranty ran out about 4 months ago but I got to talk with an apple rep who suggested (1). I reset the SMU and if that did not work, (2). Unplug all USB and firewire externals and reset the PRAM. I did the above and computer just did another uncommanded shutdown with the HP printer and external hard drive plugged back in. I do not have a problem with restart after a shutdown incident. The same issue occurred with OS X (10.5.5) and (10.5.6). The cooling fan seems to be operating at normal levels. Sleep and power saving functions appear normal. I'm currently operating with the following disconnected: 1.Lacie firewire external hard drive (time machine backup), 2. HP d145 officejet printer (USB), 3. Epson picture mate printer (USB). I have a hunch the problem may reside either with the external ports or with one of the devices. My machine has been running for about four hours now with no shutdowns. I plan to let it run in sleep mode overnight and if it does not shut down, I will try plugging in one device at a time, starting with the firewire external drive. Does anyone out there have any additional suggestions?

So much for my previous post! The G5 iMAC presented me with an uncommanded shutdown about 45 minutes later. I'm now thinking a power supply issue exists or maybe some kind of virus? The only other applicable event I can think of is that about the same time all this started happening, the APC Back-UPS unit, which the whole system is plugged into was accidently turned off with the whole system up and running. Of course everything shutdown and I had to replace the batteries in my power supply. I'm now hoping for some clues from our MAC population. Has anyone had a power management unit replaced in an iMAC, and if so, how much did it set you back? My system cost about $2800 back in 2005, but I know I can get a better one now for less bucks.

This is so weird.
My Imac G5 20" just starting turning itself off as well.
Total failure as if the power went out.
I'll try unplugging all the peripherals and see if that helps...

I'm personally thinking its the powers supply, but this seems very odd...

Hi traffic62,

Welcome to the forums.

Sorry to say this on Christmas Eve, and in response to your first post here, but "Total failure as if the power went out" almost invariably means that the power has been cut, because the power supply is failing. This is a VERY common problem on iMac G5's, especially the first generation and the '20" ALS' models.

You can eke out a little more time between the shutdowns with some of them, by reducing temps , cleaning fans and grids etc etc. as suggested above (when the power supply is failing you will find that it is very sensitive to increased temperature for a while), but almost invariably it will require replacement.

s58flame, I'm afraid you are also suffering from the same problem.

Rod

Merry Christmas everyone!

I too am having the same exact problem.
started less than a week ago. iMac would shut down for no reason— I'd hear a little pop and a black screen— dead as a doornail! I was able to get it up and running but then 2 days later it happen again.

I've zap the pram, I've reset the smu but now its shutting down after 5-10 minutes.
I heard there was an extended warranty program on the power supply from apple but it has ended.

I've swapped out memory and hard drives.
Is replacing the power supply an easy task?
If so where is a good place to purchase and get online instructions

thanks

My iMac G5 2GHz just started having this same problem too! I just put 10.5.6 on it but I can't say for sure if the problem did or did not exist before this update. I had moved the mouse one time when it was booting and I thought maybe that was it but I switched to a bluetooth mouse and the problem remains. I don't see anything in the console log that says why it shut down but then if it suddenly dies it wouldn't be able to write that information. The last thing before the restart was time machine thinning older backups.

hmmm funny im also having problems with my imac 20 inch g5
but its a little bit different then the above.

when i start my mac up i see the white screen with the apple logo en the little spinning baars for about 30 seconds and then poof its turned of tryed alot of different things but also the things written above.

please a little help on christmas (im sorry for my english im dutch)