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Model A1311 / Mid 2010 / 3.06 & 3.2 GHz Core i3 or 3.6 GHz Core i5 Processor

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Dead iMac, PSU or Logicboard?

I was called on to diagnose this dead iMac (21.5 inch, EMC 2389). Owner said she was typing something in Excel, and the whole thing just died. She had the hard drive removed so she could get her data off it. She brings it to me and I remove the LCD.

I free up the power supply and all components look OK. I plug it in and LED #1 lights up. I press the switch and there is no response, and LED #1 goes dead. Other LEDS remain dead. So, what do you guys think? PSU or logicboard?

Update (10/14/2015)

Here's an update: I measured the voltages at the PSU output to the logicboard. With the iMac on standby (just plugged in to AC), pin 4 has 12.12 V (with respect to ground) and pin 6 has 4.0 v. After I press the power button (and diagnostic LED #1 goes dead), pin 4 still has 12.12 V and pin 6 now has 3.6 V. All other pins (12 in number) read 0 or near 0 V whether at standby or after I've pressed the power button. Sounds like PSU problem?

Update (10/17/2015)

There's a label next to the black power output wiring connector covered by while glue. I have picked off the white glue, and I see 4 labels (12 or 12.1 volts+current rating) that tell what the proper voltage outputs should be. But none show which pins they should read from. So I guess the PSU is bad? Bummer.

Update (10/31/2015)

Thanks, oldturkey, here are my voltage readings:

With the set on standby, pin 4 reads 12.12 volts and pin 10 shows 4.02 volts. All other pins at the test points read 0. Only LED 1 is on.

after I press the power button, LED 1turns off, the other 3 remain off. Fans don't even twitch. The whole thing is still dead. Now, I get 12 volts from pin 4 and 3.8 volts from pin 10. I still get 0 volts from all other pins.

Отвечено! View the answer У меня та же проблема

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While this is for a different series the diagnostic LED's are the same. Technique: iMac Intel 24" EMC 2134 and 2211 Diagnostic LED's


Can you tell us what the other LED's are doing. Are you seeing any of the other LED's coming on?


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Выбранное решение

Bernie, post an image of your logic board test points. You are definitely having issues with it since you are missing some voltages:

Test Point Functions:

  • Pin 1: Ground
  • Pin 3: 5V power for Hard Drive(s). Note: If present, the 12V power will come directly from the Power Supply to the Hard Drive thru the power harness cable.
  • Pin 4: Standby 12V power (permanent power coming from power supply, present as long as AC cable is connected, even if computer is off); corresponds to LED #1
  • Pin 6: Backlight Control pulse width modulated signal (from logic board to LED backlight board, to adjust the backlight level setting according to user setup)
  • Pin 11: 12V Run-Mode power to logic board (coming from power supply, present as long as system is on or asleep); corresponds to LED #2
  • Pin12: Power On Request signal (from logic board to power supply when power button is pressed)
  • Pin 13: Backlight Enable (signal from logic board to Backlight Controller board, to enable backlight"
  • Pin 4: is about the only one that is correct.

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Which voltage needs to be read on pin 12 at the motherboard? (pin 6 at the PSU).


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Bernie будет вечно благодарен.
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