Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor

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Not Powering on Even After Replacing Power Supply (iMac 27" EMC 2429)

I initially opened up the iMac to replace the HDD because I heard a clicking noise coming from the upper middle area. However after replacing the HDD, my iMac would not turn on. With the display removed, I noticed that a clicking noise was coming from the power supply. I also noticed some discoloration around the edges of the power supply.

After replacing the power supply (purchased from iFixit), my iMac was still not powering on. Only the #1 diagnostic light was on. I tried holding the power button in while plugging in the power cord, and then pressing the power button. All the fans came on at full speed but the computer still did not boot. Still, only the #1 diagnostic LED turned on.

Trying to boot the computer without the RAM installed did not change the behavior.

Answered! View the answer I have this problem too

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I figured out the solution, but posted the question in order to share the result.

When I replaced the HDD I some how shorted out thermal sensor (not permanently), against the back of the iMac casing. This short caused the iMac to not turn on. I used an OWC Internal HDD DIY Kit when I upgraded the HDD many years ago.

iFixIt was awesome about sending me a 2nd power supply to verify I did not initally get a faulty one!!

I went ahead and replaced the power supply anyway because I figured that a clicking unit is one that may die on me soon.

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kb_me will be eternally grateful.
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