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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 can I verify which part is bad based on LEDs?

iMac 3.06 GHz 24" EMC 2267 with the 4850 HD.

Note: My issues started right after installing Mavericks.


  • iMac won't start up, often without the LCD coming on
  • No startup chime.
  • Screen intermittently will come on if I leave the computer unplugged long enough before trying to start up again.
  • When the screen does come on it will show the Apple logo and then briefly show the "rotating" startup symbol.
  • Screen flashes with some horizontal line artifacts before going off.

Further details:

I took the iMac bezel off and observed the diagnostic LEDs. There are two different scenarios for the LEDs.

  1. If the screen comes on, all 4 LEDs light up.
  2. If the screen does not come on, only the first 2 LEDs light up.

Regardless of LEDs the computer does not chime or fully start up.

I have tried to start up in Target Disk Mode, but only had limited success one time. That one time I was able to get the root directory listing on the drives, but I could not open any directories.

I have tried to start up using external Time Machine drive by holding option at startup with no change in behavior.

I tried changing the RAM to no effect. I took the RAM out and it did the beeps to indicate no RAM was installed.

Based on what I've read, this means either the logic board, video card, or LCD could be faulty. How am I to figure out which one it is? I want to think that if it were the LCD then I should still be able to start into target disk mode. Am I wrong?

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Solution retenue

Hook up an external monitor to test the video.

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. 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 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.


If you have headphones, plug them in to see if your machines sound has been muted. The Startup Chime: When you press the power button on your Mac, the first thing that happens is the Mac's hardware is initialized and the firmware -- BootROM -- is loaded and run. The BootROM is stored on flash memory chips on your Mac's motherboard, and it works as a miniature operating system to get things started before Mac OS X is loaded.

At power on, the firmware runs the Power-On Self Test (POST), which tests the processors, system memory, and network (Wi-Fi, Ethernet) and peripheral (USB, FireWire, Bluetooth) interfaces. If your hardware passes the POST, the startup chime is sounded and a light gray background is displayed on any attached display.

So what happens if your Mac doesn't pass the test? The display(s) either remain blank or off, or you might see error codes displayed. It varies from Mac to Mac, but error codes can be audible tones ("The Chimes of Doom"), flashes from external or internal lights, or a combination of those items.

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External monitor doesn't show anything.

I've read that about the LEDs, but it still leaves me in the dark. For instance, that LED #3 description specifies the video card having issues if #1 and #2 are on WITH a startup chime. I don't have a startup chime and only #1 and #2 are on which is why I'm so lost as to figuring out which part is bad. I've got really limited funds so I can't afford to order every part.


I tried headphones finally and it did not make a difference. Something odd is that the screen did stay on a little longer before it finally shut off again. It shows the startup circle a bit and then the screen flashed off. Stayed off a while then came back on. At this point the apple logo and startup circle move all the way over to the side of the screen so only half of it is showing and the circle no longer turns. It just freezes up.


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