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Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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No diagnostic #1 LED on logic board

When the computer is plugged into the wall the diagnostic LED #1 is not lit. If I leave the computer plugged in for a period on time, usually overnight the LED1 light comes on and the computer starts and runs normally.

Based on the service guide, I replaced the power supply with a new one but continue to have the same problem. I have checked the cables into and out of the power supply unit carefully and they seem good. The next step seems to be replace the logic board.

  • Any suggestions other than replacing the logic board?
  • Anything I can do to confirm it is the logic board?
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Go to Page 23 in the Apple service manual which describes to the location of the PRAM battery. I would first try replacing it as it can create some odd behaviors when its low or dead.

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What service manual and where do you find?

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iMac 27" (Mid '11) - Apple Technician Guide {'11-08-29}. He implied that was what lead him to the diagnostics. So I figured he could reference it for the PRAM. ;-}

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That is a good suggestion, tried it and still doing the same. I have a logic board on order.

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Eric Hendrickson will be eternally grateful.
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