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iMac Intel 27" EMC 2309 (Late 2009, Core 2 Duo 3.06 or 3.33 GHz) ID iMac10,1, EMC 2374 (Late 2009, Core i5 2.66 GHz or Core i7 2.8 GHz) ID iMac11,1

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iMac wont start, only diagnostic led 1 on

My imac wont give any sign of life.

Only the first diagnostic led is on when connected to power. Nothing happens when i press the button.

Does this mean my logic board is broken? Cause replacing that is way to expensive.. :(

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Hello Casper. Years later, on my 2015 5k, same issue. Did you figure out what it was?


Jordan - The newer iMac's are more sensitive to power surges. Often burning out the power supply which is what the onboard diagnostic LED is telling us here when only the first LED is lit. In some cases the logic board gets damaged too!

I would replace the power supply and hope! In any case I do strongly recommend getting a fill-in UPS for your system and its peripherals. You should also check the outlet is wired properly and grounded to the breaker panel and the buildings ground is in good shape.


The display cable port got broken. I brought it to the Apple store because the fans were always full on. they gave it back saying they won't touch it because they found out it was opened by someone "uncertified". When I got back the iMac didn't turn on at all. Brought it to an expensive repair-shop and they found out the port got broken. (Thanks Apple Genius.. :/ ) They soldert a new one on and it worked again.

Not sure this is of any help to you.


OK- quick question. In a nutshell. My 5k has no backlight and I've ordered a working logicboard and power supply to switch out and test. When I was trying the different parts in place I got different results than we I finally gave up and put all the components back in place and plugged in. The question is, do you have to have everything plugged back in place in order to get an accurate result? In other words I tried to just hook up the main board, power supply and fan and things didn't seem to work the same when I hooked all the components back up. Sorry if that was confusing but this is KILLING ME! ha. Thanks


I have almost the same issue, however in my case LED also goes out when I press the power button, and nothing happens.

Any ideas what can be the reason?


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Casper Smit, that sounds like it would be a very drastic replacement. The very first thing I would do, is to check this out:"

LED #1

• 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 and that logic board voltage regulators are functioning properly. 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

• Indicates that the computer and the LCD 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 display, then the LCD panel, the LED backlight board, or the cables between might be installed incorrectly or need replacement.

LED Startup Sequence

LED #1 = Power available.

If no LED is visible:

• Verify AC source

• Verify known-good AC cable is connected

• Verify cable connection between AC inlet and power supply

• Verify cable connection between power supply and logic board

• Verify power supply

'''LED #1 + LED #2 = Power available, and system is powered on.

If second LED is not visible when power button is pressed:

• Verify power button connection to logic board

• Verify power button functionality

• Verify cable connection between power supply and logic board

• Verify power supply

• Verify logic board

And as you see, the logic board is on the bottom of the list of items to replace. I would start by checking all connectors and cables, and if you need to replace anything start with the power supply. Do check the capacitors on the PSU, make sure that they are not bulging or leaking. That would be an easy fix.

My usual disclaimer of course is that I am not a Mac person and I am sure that the Mac gurus can help you more than I can. Good luck!

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Thnx for the reply!

Any idea on how to verify power button functionality?

Its my last hope i guess..


They have diagnostic led's now when I owned a MacBook they didn't


I'll say this. I resurrected mine by replacing the entire main board. I found someone on eBay selling them for a great deal. Keep your eyes open there. Mine sat for years and I wanted to give it one more shot and it works fine now.


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