Not Starting, Motherboard or Video Card?

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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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laurentoma @laurentoma

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Posted: Oct 12, 2014

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Not Starting, Motherboard or Video Card?

Hello everybody,

I have just been given an iMac 20" from 2008 that does not start. When I press the power button, I can hear the startup Chime every 5 seconds since it keeps rebooting. I can also hear the fans and optical drive. However the screen remains black.

I took it apart and I only have led 1 and 2 on. Both 3 and 4 remain off all the time. (led 3 is on for half a second when I press the power button)

As I am now trying to figure out if it is a motherboard issue or a video card issue, I am in need of your help since both parts can be quite pricy compared to the value of the computer.

The motherboard is a "820 2223 A" and the video card is an ATI "109-B22553-11".

Thanks in advance

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mayer @mayer Rep: 685.3k MacHale Enterprises 3.4k 1.1k 2.6k · Answer 1 · 2016-02-10T09:17:50-07:00

LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. 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 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.

iMac Intel 24" EMC 2134 and 2211 Diagnostic LED's