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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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iMac 27" power stays on without the LCD assembly

Hello everyone,

Computer guy here and repaired all kinds of Apple iMacs... This iMac 27” puzzled me to no end.

I’ll do my best to explain…

  1. If I powered up the iMac it will shutdown within seconds (it will show the white screen and the Apple chime before shutdown).
  2. The iMac won’t come on again unless I unplugged the power cord for few seconds. Try again and the iMac will power up/shutdown within seconds. Yes. I have replaced the power cord.
  3. Here is the kicker… after I removed the LCD assembly along with the usual wires/cable/graphic ribbon etc; I can powered up the iMac, hear the Apple chime and it continues to run just fine for hours.
  4. As soon as I restored the LCD assembly, the iMac goes back to shutting down within seconds.
  5. Could that be the backlight invertor or the main power pack? I am guessing there isn’t enough power? The power pack gets weaker etc?

Looking forward to any suggestions you may have.

Thank you

Answer this question I have this problem too

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If unplugging the display makes a difference then its more likely a short in the T-CON or the backlight LED bar - The display

Time to try a second display assembly

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3 Comments:

Thanks for your suggestions... Luckily, a customer is coming tomorrow with his working iMac 27" for servicing. I'll see if his working invertor makes a difference.

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@techmanuk - So you'll replace the engine of the car even though the issue is the window is broken??

Why are you not focusing on the part that causes the failure. Its not the engine in my example its the window!

From what you state its not the inverter!! If the display is not wired to the system as you described then it can't be the converter. Hence why are you changing the engine out when the window is broken??

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Misread the above comment regarding the backlight LED bar.. will swap the LCD display

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MrRoberts will be eternally grateful.
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