Unplanned Shutdown

I am having problems with my iMac unexpectedly shutting down. I have had this problem for a while (years) but it has gotten dramatically worse to the point where it is shutting down 3 times within a 10 minute span. I have tried moving the power cord to trigger the shutdown but nothing happens. I have ran programs like istat nano, S.M.A.R.T. Utility and Disk Utility but I am not sure how to correct the errors they might find. I don't know the cause of this problem. I am trying to get a presentation ready for a wedding using iMovie but it is proving difficult when the computer shuts down every 15 minutes. I am out of my Apple Care Warranty and would like to avoid the $50 service fee if possible. I am not sure if it is a overheating issue, hard drive failure issue, or bad RAM. If there is a test, I can run it and post the results as quickly as I can. Here are some basic stats about my iMac

OS: 10.6.7
Processor: 2.4 GHz Intel Core 2 Duo
Memory: 2 GB 667 MHz DDR2 SDRAM
HD: 100 GB free

Temperatures (in F) from istat right after a shutdown:
HD: 126
CPU: 121
GPU: 139
GPU DIODE: 142
GPU HEATSINK: 139
AMBIENT: 81
MEMORY CONTROLLER: 124
AIRPORT CARD: 148
HD BAY: 122

With those temps I'd pretty much rule out thermal shutdown. Have you tried resetting the SMC?

Replace CMOS. Have seen many that will report erratic issues, even failed CPU diagnostic lights. OSX is not kicking in that "old chestnut" any more that "your time and date are set incorrect" this will cause erratic behavior if not addressed.
Regards

Dysfunction,

I have tried resetting the SMC and I still have the issue of unexpected shutdowns.

powermac G5 said:

Replace CMOS. Have seen many that will report erratic issues, even failed CPU diagnostic lights. OSX is not kicking in that "old chestnut" any more that "your time and date are set incorrect" this will cause erratic behavior if not addressed.
Regards

Click to expand...

I am assuming that you are referring to the PRAM or logic board battery? I have not had any issues with my time and date being set incorrectly that I am aware of. I was researching the CMOS and it seems that is in the G3 imacs. I was looking at the battery info and it seems that it is linked to the Power Management Unit. I just want to make sure before I open the hood on this intel imac.

I doubt seriously it's an issue with the PRAM battery. Unexpected shutdowns are almost always related to hardware. The two things that most likely cause shutdowns as you're having are bad memory or a flaky power supply. It could also be caused by a bad logic board.

Since the memory is easiest to check, start with that. The power supply is going to require technical ability to trouble shoot and is difficult to access. Any kind of maintenance (other than memory replacement) on an iMac requires that the display panel be removed first.

It may be best to let an authorized Apple service center do the trouble shooting and repair if it turns out not to be a bad memory module.

And to add to the above post, dust will also cause problems and iMacs are not the easiest to crack and clean.

chscag said:

I doubt seriously it's an issue with the PRAM battery. Unexpected shutdowns are almost always related to hardware. The two things that most likely cause shutdowns as you're having are bad memory or a flaky power supply. It could also be caused by a bad logic board.

Since the memory is easiest to check, start with that. The power supply is going to require technical ability to trouble shoot and is difficult to access. Any kind of maintenance (other than memory replacement) on an iMac requires that the display panel be removed first.

It may be best to let an authorized Apple service center do the trouble shooting and repair if it turns out not to be a bad memory module.

Click to expand...

So I ran memtest tonight and everything passed when I did the single user mode. I rebooted the computer and upon the reboot, it shutdown. I guess it has to be something other than the memory. I assume that there is not a way to test the power supply or the logic board. I have already tried Apple Hardware Test Extended and it said everything was fine.

chscag said:

I doubt seriously it's an issue with the PRAM battery. Unexpected shutdowns are almost always related to hardware. The two things that most likely cause shutdowns as you're having are bad memory or a flaky power supply. It could also be caused by a bad logic board.

Since the memory is easiest to check, start with that. The power supply is going to require technical ability to trouble shoot and is difficult to access. Any kind of maintenance (other than memory replacement) on an iMac requires that the display panel be removed first.

It may be best to let an authorized Apple service center do the trouble shooting and repair if it turns out not to be a bad memory module.

Click to expand...

Replace the CMOS/PRAM battery/Back up battery, what you guys call it, you know what I speak of, replace the battery trust me
I buy pallets of salvage macs and refurbish for resale. This puts food on the table and a roof above and to be perfectly honest I have replaced CMOS batteries in 2006 Mac Pro that report errors with cpu's deemed by apple to have failed logic boards, battery is dying. OS X does NOT pick up everything.
Tell me have, you seen time and date not set with SL? Your computer will act erratically as 10.5 would show, hence even unexpected shut downs. No matter if a hardware issue you will be opening the mac to inspect, start cheap and replace that silly back up battery that every one neglects.

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