Why is my iMac shutting down randomly?

Question

iMac Intel 20" EMC 2133 and 2210

Model A1224 / Mid 2007 and Early 2008 / 2, 2.4, or 2.66 GHz Core 2 Duo processor

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Thomas @thomas42689

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发帖于: 2013年5月12日

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Why is my iMac shutting down randomly?

Hello everyone!

4 months ago my 2008 imac 8.1 20" EMC 2210 started shutting down after it had been working for about one hour.

Right now its shutting down after 30 minutes, but sometimes much faster..

When is shuts down, first the screen goes black, but the system keeps on going. A couple of seconds later everything just shuts down and the computer tries to reboot a couple of seconds later..

The diagnostics LEDs, all 4 of them are on when the iMac is running. As soon as the screen goes black, the 4th LED goes out. After a couple of seconds they all go out, except for the first LED.

I have done the following:

- Cleaned the fans

- Checked the RAM

- Booted in safe and single user mode

- Performed a hardware test, no issues

- Hardware test uitgevoerd, geen issues

- Tried smcFancontrol for keeping the CPU temperature low

- SMC reset

- PRAM reset

None have showed any improvements.. Although when using a fan on the back of the iMac it seemed to last a bit longer..

Does anyone have an idea?

Thanks!

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Is it stable in safe or single user modes? If not try dimming the display brightness to as low a level thats possible that you can see see the display. Does the system run longer?

由 Dan 完成的 2013年5月12日

Hey Dan, its not stable in single user or safe mode. I'll try to dim the screen and check it! Thanks

由 Thomas 完成的 2013年5月12日

Okay Dan, lowering the brightness didn't have any effect on the problem..

由 Thomas 完成的 2013年5月12日

Running advanced AHT once is often not enough run it 2 or 3x in succession. Also have you looked at your crash logs? Crash logs can often point you in a direction, or rule out an erroneous assumption.

由 originalmachead 完成的 2013年5月12日

Do you have access to an external Firewire HD which has a working system on it? If you do alter the startup disk to it and restart running off it it. Is the system stable now? If not, its starting to look like either a power supply or logic board problem.

由 Dan 完成的 2013年5月12日

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Dan @danj

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Once you get the external monitor connected keep an eye on it so when the internal display dies is the external still running before the system restarts. If you still have an image then the display is bad if it doesn't then the power supply is bad.

While your at it I would pull the heat sinks off and apply a fresh coat of thermo paste on both. Given the age of the system this will help keep it cooler.

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Hey Dan,

Couldn't it be a logic board issue too? Just wondering, because if I purchase a new power supply and it isn't the problem I would have wasted a lot of money..

I checked the voltages of the power supply according to this link (iMac Intel 20" EMC 2210 Power Supply Output Voltage Test) and all the voltages match, except the standby voltage of PIN 5 which should be 3.8 V but its 2.6 V instead..

When the imac is plugged in, but not on I also hear a very silent ticking noise, which isn't 50/60 Hz...

Thanks!

由 Thomas 完成的 2013年5月13日

What did you see? Did both displays go out on both at the same time? The only thing left is the GPU (which is part of the logic board) Vs Power Supply. You ruled out most of everything else here. Your measuring of the voltages also points to the Power supply.

由 Dan 完成的 2013年5月13日

FWIW A thermal paste refresh is a major, advanced DIY - though at this point the machine is almost useless anyway so if you kill something in the process it's not really a "loss".

由 originalmachead 完成的 2013年5月14日

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Is it stable in safe or single user modes? If not try dimming the display brightness to as low a level thats possible that you can see see the display. Does the system run longer? — Dan
Hey Dan, its not stable in single user or safe mode. I'll try to dim the screen and check it! Thanks — Thomas
Okay Dan, lowering the brightness didn't have any effect on the problem.. — Thomas
Running advanced AHT once is often not enough run it 2 or 3x in succession. Also have you looked at your crash logs? Crash logs can often point you in a direction, or rule out an erroneous assumption. — originalmachead
Do you have access to an external Firewire HD which has a working system on it? If you do alter the startup disk to it and restart running off it it. Is the system stable now? If not, its starting to look like either a power supply or logic board problem. — Dan
Hey Dan,

Couldn't it be a logic board issue too? Just wondering, because if I purchase a new power supply and it isn't the problem I would have wasted a lot of money..

I checked the voltages of the power supply according to this link (iMac Intel 20" EMC 2210 Power Supply Output Voltage Test) and all the voltages match, except the standby voltage of PIN 5 which should be 3.8 V but its 2.6 V instead..

When the imac is plugged in, but not on I also hear a very silent ticking noise, which isn't 50/60 Hz...

Thanks! — Thomas
What did you see? Did both displays go out on both at the same time? The only thing left is the GPU (which is part of the logic board) Vs Power Supply. You ruled out most of everything else here. Your measuring of the voltages also points to the Power supply. — Dan
FWIW A thermal paste refresh is a major, advanced DIY - though at this point the machine is almost useless anyway so if you kill something in the process it's not really a "loss". — originalmachead

Ashley Ryan @ashleyryan 声誉积分: 5.5千 20 17 12 · Answer 1 · 2013-05-12T18:11:49-07:00

Ashley Ryan @ashleyryan

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You may have a power supply issue. Also, if smcfancontrol says the temperature is a really high one, that could be your problem.

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It could very well be PSU issue, but all the light are on correctly.. I think I'm just going to take the multimeter and check the voltages coming out of it!

smfFancontrol doesn't indicate any temperatures that are too low, I just tried it to try and keep things cooler but that dind't affect anything..

Thanks.

由 Thomas 完成的 2013年5月13日

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