Testing a power supply

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iMac Intel 21.5" EMC 2428

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

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Adam @moon_man157

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发帖于: 2016年7月14日

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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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Dan @danj

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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?

由 Adam 完成的 2016年7月14日

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

由 Dan 完成的 2016年7月14日

iMac Intel 21.5" EMC 2428 電源更換

iMac Intel 21.5" (Late 2009-Mid 2011) Power Supply

由 mayer 完成的 2016年7月14日

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.

由 Dan 完成的 2016年7月14日

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.

由 mayer 完成的 2016年7月15日

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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? — Adam
Yes, the soft switch logic is on the power supply unit not the main logic board. Review the info in the link ;-} — Dan
iMac Intel 21.5" EMC 2428 電源更換

iMac Intel 21.5" (Late 2009-Mid 2011) Power Supply — mayer
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. — Dan
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. — mayer

iMac Intel 21.5" EMC 2428

Testing a power supply

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