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Model A1311 / Mid 2011 / 2.5 & 2.7 GHz Core i5 or 2.8 GHz Core i7 Processor

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Not Turning On Suspect Faulty Power Supply

Hi All,

I have a Mid 2011 Imac 21.5 inch 2.7ghz Corei5 EMC: 2428 that won't turn on and I suspect it is a bad power supply.

No lights on the logic board.

Please tell me how I can test to see if it is actually the power supply and not the power chips on the logic board or something else that may be the culprit before I purchase a new power supply from ifixit?

Thank you in advance.

Ben

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There should be four Diagnostic LEDs just to the right of the RAM slots on the logic board. If you get none or just a lite on #1 replace the power supply first. Also check the power outlet from the wall and make sure the power cable is plugged into the wall and back of the machine.

LED #1

Indicates that the trickle voltage from the power supply has been detected by the main logic board. This LED will remain ON whenever the iMac is connected to a working AC power source. 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 source 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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Hi Mayer, Sorry I did not see your Answer before I posted a comment to MacOS Genius below. So far I can only see that led light # 1 is on and I have tried all of the steps he mentioned with no luck. I also see 12 volts on the multi meter when I test the solder points to the left of the led lights and also 4 volts on two sets of pins on the power supply and then 12 volts on two pins lower down on the power supply. Would it now be a faulty logic board?

Should I just get a replacement power supply first and hope it is only that and not a logic board or other part that may also faulty?

Please let me know what you think.

Thanks.

Ben

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Yes, that's the logical first step. You can always return it if it's not the issue.

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Hi Mayer, Thanks for your reply. Is there a correct way to test the power supply with a multi meter to rule out whether it is faulty or not before purchasing as I am in Australia and it will take some time for the part to get here and if it is not the power supply I will have to ship it back, etc... Could it also be the power chips on the logic board or something else? Or are you hinting that it is almost always the power supply that is to blame in most cases and getting a new one is the proper course of action? I am sorry for asking so many questions and I really appreciate all of your help .

Thanks.

Regards,

Ben

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You could try to measure the voltage if you have the experience to do it ( On the powersupply).

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Hi mathiasaat,

Thanks for that info. I do have a multi meter but I am unsure of which points to place the red and black leads to?

Do you know or is there a video of how to perform this task?

Thank you.

Ben

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Hello Ben,

Well there are a few troubleshooting steps you may of done already though you can follow these steps and get back to see where you are to your device i have several here in my school and do this every once in a while and when I perform these tasks those processes our Macs power back on, but lets see what happens.

1. Verify AC power source plug another device to wall outlet or plug

2. Disconnect all peripherals and press and hold power button for 15 seconds, this is performing an SMC Reset.

3. Verify user's power cord and have one available to replace if helps

4. Determine if computer is in power-on state by checking all of the following : (When i do this i press the power button a good second and then wait for a good 30 seconds and it turns on.

Caps Lock LED on wired keyboard

Fan spinning sound

startup sound

hard drive spin (if hard drive present)

optical drive reset/disc detect seek

display backlight on or flash

external display activity, if available

Thunderbolt disk mode operation (on newer models)

if the steps above did not resolve the matter and unit is still off, try the following with only the basic connections usb keyboard and mice corded prefer and power cable.

Performed the SMC Reset unplug all devices and press and hold power button for 15 seconds and then leave unplugged for up to 1 hour recommended, but 30 minutes will do fine - just that apple recommends an hour and understand the power supply contains a high voltage capacitor that may remain charged so performing the SMC will assist in this process.

If this process fails please perform the same process with a different power cord and outlet, if unit still fails

Locate the Diagnostic LED's on logic board With AC power cord connected to computer, verify whether diagnostic LED #1 is on, indicating power supply is providing power to SMC and logic board.

  • If there is no power LED after performing an SMC Reset, result is a power supply
  • If there is power led, Verify that the DC power cable and HDD power cable are plugged into the correct ports on the logic board. These cables have identical connector ends and could accidentally be switched.

You can differentiate these cables by the length of the wires between the connector and sheathing. The HDD power cable has more length of exposed insulated wires between connector and sheathing than the DC power cable.

And Finally since the unit is open you can Remove coin battery and AC power to computer. Wait 90 seconds, then restore AC power and attempt to power on computer.

  • Note: On some iMac models, the coin battery is located on the back side of the logic board.

If unit still does not power on you are now at replacing the power supply or logic board, if you want to go more detail tell me what works as there are 3 more steps.

Thanks

www.MacOSGenius.com

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Hi MacOS Genius,

Thanks so much for these tips.

So far I can only see that led light # 1 is on and I have tried all of the steps above but still no luck. I also see 12 volts on the multi meter when I test the solder points to the left of the led lights and also 4 volts on two sets of pins on the power supply and then 12 volts on two pins lower down on the power supply. Would it now be a faulty logic board?

Please let me know what you think.

Thanks.

Ben

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