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Model A1200 with 2.16 or 2.33 GHz Core 2 Duo processor

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Need help with boot failure issue.

Screen stays dark. Power light lower right comes on. 3 Fans turn. I get three of LEDs on the logic board briefly, then only two. Sometimes the optical drive makes a cycling sound.

Tried two replacement logic boards with similar results, except for the optical drive cycling, which may or may not occur. Not predictable.

Tried replacing the video card, no difference.

This occurred after a mains power failure to the home.

Unit is EMC 2111

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Apple iMac "Core 2 Duo" 2.33 24-Inch Specs

Identifiers: Late 2006 - 24" - BTO/CTO - iMac6,1 - A1200 - 2111

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Probably doesn't matter. But, this particular unit is the 2.16 version.

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Hook it unto an external monitor and see if a video signal is being generated.

LED 1 indicates that trickle voltage from the power supply has been detected. This LED will be ON when the computer is turned off and your power supply is working correctly.

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 LCD display are communicating. This LED will be ON when the computer is turned on and video signal is being generated.

LED 4 lights only if the computer detects an over-temperature condition. This LED will be OFF when the computer is turned on and running at the correct temperature.

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Thanks for the info. I hadn't tried an external monitor before. But that screen is dark, too. That with no LED 3 would indicate no video signal, I guess. Strange it behaves that way with two different video cards and 3 logic boards. (None of which I can prove are good.) I should add that I don't hear any disk drive activity that would be heard during a normal boot process. About once a minute the optical drive cycles. I don't have any media in it, though. Wish I had schematics so I could probe test points for clues. I hate to scrap the machine. I'll take out the hard drive and test it separately. But, I don't see how a hard drive fail would block the video.

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Lloyd O will be eternally grateful.
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