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Model A1225 / Early 2009 / 2.66, 2.93, or 3.06 GHz Core 2 Duo processor

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How come my iMac keeps shutting down after these tries to fix?


I have a 3-year old iMac 24-inch aluminum and some time ago, while i was Skyping with my girlfriend, he just shut down like the power cable was pulled out of it.

After this I turned on my iMac again and it kept shutting down without any warning.

Have been searching the internet many times about how to fix this and this is what I've done by now:

- Booting in OS X from external HDD (verifying if it was HD related)

- Removed the internal HD and booted from the external one

- Replaced RAM with brand new ones

- SMC reset, PRAM reset, VRAM..

- Several Apple Hardware Tests, short and extended for several hours (no problems found). Note that the iMac NEVER shut down while performing these tests.

- Full clean install on the internal HDD itself

- Performed Repair Disk and Disk Permissions

- Created new user, logged in with that account (no luck either)

- Checked the Power Cord for any damage AND switched to other wall sockets

- Installed smcFanControl and turned the fans to full speed so it got cool enough (still shutting down)

- Installed SystemLoad and performed those tests while monitoring the temperature with TemperatureMonitor.

- Dismantled the iMac (since I'm out of warranty), cleaned out the fans, vent from CPU. Pulled out the PSU to check if something was burned through.

- Checked the diagnostic LED's on the logic board.

> LED #1 is on when iMac is off;

> LED #1, #2, #3, #4 are on when the iMac is on.

All of these things did NOT fix the problem! I'm out of desperate tries and as a university student, i don't have enough money left to buy a new one nor, because I'm out of warranty, fix it due to the high costs.


Hi there! Unfortunately the iMac is still not repaired. I have completely dismantled the iMac and replaced the thermal paste of the CPU and GPU but still no luck.

I notice that the display gets really hot on the top left corner after 5Mins. while the iMac is in stand-by. I don't have to open any programs or what so ever to make it hot after 5mins. .. while the iMac is up and running, all 4 LED lights are on but i get an image, i can just work on the imac without problem until it just turns itself off.

So i don't know which comment to follow, is it a temperature problem or something else? No idea...

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4 Yorum

Glenn - Try altering the display brightness to the lowest to see if the system runs longer. Let us know what you discover.


This iMac used CFL's to light the display. It's likely the Backlight circuit which is part of the display assembly is overheating


Mine is a 2010 iMac. It was finally diagnosed as a failing motherboard (or whatever Apple calls them) and power supply. We found out from someone that worked for Apple that there was a design flaw in these computers. The bracket that holds the hard drive was not far enough away from something running across the bottom. Apparently, Apple replaced so many parts that they just quit making replacement parts for this model. Mine is now toast. It's a shame that a computer is obsolete after only six years. (It's been shutting down for over a year, getting worse all the time)


obsolete after 6 years how long do people expect a computer to last for? you pay $XX,000 of dollars for a car, not including maintance. and it last about 6-10 years. I wouldnt expect much more out of a $2500 machine. i do agree its a shame but its just how everything is now a days. 6 good year is better than any years with a crappy pc : )


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Try this: Turn down the displays brightness to the lowest setting that you can still see the desktop. Do you find the system is now staying up or running longer than before? If you do your display has a problem.

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Mhm that's something plausible. The thing is that, ever since i bought the iMac i never was able to lower the display brightness to dark or almost dark (like you can on a MacBook). So i don't know if that's normal on iMacs or maybe that's one of the signs that my display had a malfunction all along?

The lowest brightness I can go on my iMac is like the medium setting of brightness on a MacBook (on my Macbook Pro it's like 7-8 presses on the key after first fully go dark, then pressing the brightness key 7-8 times to get brighter).


While that is useful to know the display can't dim that far, the real Q here is if the lowest setting improves the time before the system shuts down.


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LED 4 indicates that the iMac is detecting over temperature conditions

That is not correct on this model of iMac:

LED #1 (left-most)

Indicates that the trickle voltage from the power supply has been detected by the main logic board. This LED will remain ON whenever the iMac is connected to a working AC power source. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power source is disconnected or the power supply is faulty.

LED #2

Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

LED #3

Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.

LED #4 (right-most)

Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.

Did you ever get that machine to work?

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The location you describe as hot is where the psu sits. Try to take it to someone who can test all the voltage rails, maybe something is gone bad. I had an similar problem on a late 2009 27" i5 iMac, but we figured out that GPU overheating was the cause (this machine shuts down when the gpu die hits 80 degrees Celsius).

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Do you heasr your fans kicking on..... if not, change the fan!

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I've ran into the same problem with my 24 inch iMac but come to find out the problem was with my video card. After the card started getting hot it would shut down my iMac . this is pretty common with iMac MacBook pros laptops there's two ways to fix it. One replace the video card which can be expensive or two reset the video chip on your video card . That will require you to bake the video card for about eight minutes at 350° if you're not technically inclined with breaking your Mac down I would not attempt it.

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@hns357 - This is a very old question so I'm sure the OP has long since fixed their system (replaced his display).

As to baking do you baste it in butter as well ;}

Sorry guy while some have made claims of baking in solving their problems the temp needed here would need to be hotter to melt (effect) )the solder. Just warming it up won't do. More likely the action of taking it out and putting it back in altered things.

In any case fixing a cold solder joint or a tin whisker problem using an oven won't be permanent. You see the solder holding the chip has degraded and needs to be cleaned off fully and the proper solder then needs to be re-applied.

Then there is the interconnections within the chip which on some have known to fail which you can't fix.


Get yourself baked first, then bake the card in the oven. Let's see how that works out.


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Go back to pc. I have been a mac fanboy for 7 years and since the death of Steve Jobs apple has been living off its former reputation and Iphone. No new next big thing , quality has gone down hill , no touch screen, even customer service is not what it use to be. I am going to give microsoft another try . I tried a friends 27 inch HP envy and was very impressed.

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I will never do Microsoft again after their system they said was perfect running crashed and destroyed two generations of my family photos and I lost thousands of songs from my music library. Went to a mac laptop and it ran perfectly until the back light died on it. Then I have my iMac 32in. It still works perfectly and is a 2009 model. A little slow, but she still runs. My mobile computing is done with my Acer Chromebook. That thing is faster than most any Microsoft that tries to run with it. Plus it will always be virus free like the apples. Compared to Microsoft, that is far better.


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It seems to me that you may have a defective temperature sensor in your machine. LED 4 indicates that the iMac is detecting over temperature conditions, which are caused by dusty vents (ruled that out) or defective temperature sensors. During normal operation, LED #1 #2 and #3 should be on, and LED #4 off. You will want to go through the iMac and make sure that all the temperature sensors are properly connected and are not damaged. If the problem persists, then you will need to get a set of replacement temperature sensors. You can usually find sets on eBay or amazon for pretty cheap.

Hope this Helps

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Hi! Thanks for your comment here.

A friend of mine suggested to install Windows through Bootcamp and not install any video drivers to cancel out the fact that i'm having a faulty video driver. This is what I did and my iMac now is already working for 40mins. I can still see the #4 led light on logic board burning. So the next thing i did was installing SpeedFan.

The temps show

- HD0: 39°C

- Core0: 23°C

- Core1: 21°C

although the iMac feels hot on the screen, these temps are, in my opinion, really low. None the less, i can see these temps fluctuating so not sure if these are totally damaged or not.

I live in Belgium and already looked up on ebay to buy new temp sensor cables but only 1 cable will cost me 30 euros! And without knowing which cable it is, or even if this is causing the problem, I'm not sure what to do.

Is there maybe any way of checking which temp sensor cable can cause the problem?


You should be able to do a voltage get on the temp sensors to see if they are getting any current to them


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