iMac Intel 27インチ EMC 2309 (Late 2009, Core 2 Duo 3.06もしくは3.33 GHz) ID iMac10,1, EMC 2374 (Late 2009, Core i5 2.66 GHzもしくは Core i7 2.8 GHz) ID iMac11,1

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27" iMac suddenly won't turn on… completely dead? (late 2009 2309)

Model: Late 2009 iMac 27" A1312 2309 (Core 2 Duo)

Need some help please! I woke up one morning recently to find my iMac was dead to any input. It was working fine the night before, I didn't shut down and just let it go to sleep on it's own. There is zero response when the power button is pressed, no boot chime, no screen response, no fans/hard drives spin… nothing.

What I've tried so far:

  • Different power sockets, different power lead
  • Reset SMC
  • Replaced PRAM battery
  • Replaced iMac power supply
  • Removed graphics card

There is only one diagnostic led lit on the logic board (labelled LED601) when the iMac is plugged in:

Block Image

There are 4 LEDs in total and it's the led furthest from the board edge that lights up. Strangely the service manual for this model seems to list the LEDS in an opposite order to my board:

Block Image

I assume the LED that is lit up must be LED 1? ( indicating that trickle voltage from the power supply has been detected by the logic board).

Does this mean that it's most likely a logic board fail? why would the logic board suddenly fail overnight when iMac was sleeping?

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I have exactly the same problem; changed the power supply, but nothing.

Where can I find the diagnostic LEDs? So that I could have a check?

J. Willemsen


The lights are to the right of the RAM slots on the logic board.


How long did you hold the power button? Try keeping it depressed for about 1-2 minutes......



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Hello everyone. Just wanted to post what worked for me. I went through all the official mac steps, nothing worked. Dug deeper and found a "fix it yourself" step by step. It suggested pulling the RAM and then try starting the computer. This worked- The fans came on and the mac steadily beeped (indicating 'no RAM'). Now, one by one I replaced the 4 chips and started it up expecting to find a bad one that was causing my original problem. All 4 are back in and the mac is running just fine!?!? I hope this solution finds you. :0)


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@rudenator: YOU SAVED MY DAY (see below)

Thank you


I had exactly the same scenario listed above. A dead iMac, unresponsive to the on/off switch. Switched out all the cables etc with no fix.

I can confirm that removing the Ram boards (easy to do - just unscrew the bottom compartment) - pulled them all out - put them all back in - and hey presto - it worked.

Good Luck




Replace the power supply.


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I did that already, and it had no effect.


Check the source of where that power supply came from. Sounds bad to me.



The "suddenly won't turn on" thing happened 2 times before throughout the years (I have it since late 2009...), so every time service would't find anything better than replacing the motherboard - which is f***ing expensive.

So I tried this time what @rudenator suggested, and YES !

In detail, all 4 memory slots were taken. Since some time, I had a doubt about it, as system diagnosis showed up only two ram in place. But so far the iMac worked fine, and I omitted to check physically if I was crazy or if the 2 ram had disappeared somehow.

In reality, the two "missing" memory bars seemed to be broken, and yes, they were still in place, they simply didn't show up. These two were in the BOTTOM emplacement. I took them out, as I guessed they were defective since a while.

Next I tried the two remaining individually in the TOP emplacement (relative to the screen which is top). This, because after Apple a single ram can work in the TOP place, but not in the bottom, at least for this model.

THE iMAC REBOOTED with one of them !

Next, I checked them all individually, and in fact even one of the former bottom ram still worked. YES.

I explain myself what happened, by the fact that if you pair a working with a non- working ram diagnosis thinks they are broken both, so if they are in bottom the machine don't shows them, and in top the machine won't boot.

I dont know, but maybe this trying saved me from a new motherboard...(which I wouldn't have paid, as the iMac is 8 years old now), but at least it saved me from buying new ram.


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Found this thread troubleshooting a similar problem. iMac would not turn on one day. Power Supply is providing voltage to the logic board - LED 1 is lit (very difficult to see on the very first 2009 21.5 iMac model but I get voltage at pins 1 and 4 on the logic board). After reading this thread I pulled the RAM (as a side not this iMac and the RAM compartment were very dusty and full of fuzz which I blew out after pulling the RAM). The iMac did power on although there was no chime and no error beeps (note that the display was not installed). Just fans on high. I turned it off and turned it back on several times and got the same result each time. When I tried reinstalling the RAM one by one I would get nothing. Thinking the RAM or slots were bad I tried once more to power the machine with no RAM and I am back to a no power situation again. I have not checked the PRAM battery - for some reason Apple put it on the back side of the logic board which means a complete disassembly just to check it. Or, does anyone know any way to check the PRAM voltage without exposing the actual battery? Are the pins accessible from the front? Anyone with any other ideas - I’m all ears.


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Shane Murphy さん、ありがとうございました!

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