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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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Testing a power supply

My iMac will not power on, the diag LED’s do not turn on ether. I’d like to test the power supply independently of the logic board. I know how to cross pins on a standard ATX power supply and verify functionary but they have 20 pins and most are color coded. The power supply in the iMac only has 14 pins and there are no voltage or polarity markings I can see. I’ve looked quite a bit online and have been unable to find a pin-out of the EMC 2428 iMac power supply. Can someone please point me in the right direction?

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If the diagnostic LED's aren't lighting up and you're sure you have a good cord and power at the outlet it's a slam-dunk here your power supply is gone, time for a new one.

Diagnostic LED’s

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Thanks Dan.

Yes, I’m sure the A/C to the power supply is good and just for good measure I tested the power button. The power button is fine but I thought something might be wrong with the logic board which might stop the signal from getting to the power supply. Are you saying that if the power supply were good there should be some responds from the diag LED’s no matter how bad the logic board may be?


Yes, the soft switch logic is on the power supply unit not the main logic board. Review the info in the link ;-}


Thanks Mayer for adding the links!

I should add many power supplies get killed by bad power or lightning strikes. Best to get a good surge suppressor or a UPS. We opted for UPS's, we saw a dramatic reduction of burnt PS's.


A UPS can also prevent hard drive writing errors. I found this especially true in old parts of town where power supply lines or transformers don't supply a clean steady flow. If you get the lights dimming when air conditioners come on, you have a probable issue with this.


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Adam будет вечно благодарен.
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