Model A1225 / Mid 2007 and Early 2008 / 2.4, 2.8, or 3.06 GHz Core 2 Duo processor

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iMac caught in reboot loop. LED #3 flashes before reboot

Hi, My iMac is playing up and won't boot. I've pulled off the screen and notice that LED 1 & 2 are fine but LED 3 flashes on when the boot tone sounds then the computer resets. LED 4 never lights.

I've videoed the process here: https://youtu.be/RuACtKfZkMw

Any ideas what needs replacing?

Serial YM815OU4ZE4

All suggestions apprecited

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Apple iMac "Core 2 Duo" 2.8 24-Inch (Early 2008) Specs

Identifiers: Early 2008 - MB325LL/A - iMac8,1 - A1225 - 2211

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Looks like a bad video card. What happens on the screen? Do you get anything with an external monitor hooked up?

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.

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Thank you, I'll try to borrow a mini display port cable to test on the TV. My suspicion is that it'll continue to reset with the external monitor attached.

As this website doesn't have an exact match for a video card replacement guide for the 2211, can you suggest which guide is closet match?

Is there anything else I can do to confirm that replacing the video card will fix the problem?

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