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Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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New Power Supply - iMac goes into Sleep mode

Just installed a new power supply in my mid 2011 Imac 27. Upon powering up, within a few minutes the imac goes into sleep mode, it seems. If I hit a key, the screen comes back up. When the screen goes black (what I believe is sleep mode as stated above), I can hear the fans also shutting down. After relooking at everything, a few times, I reinstaleld my old power supply. The Imac started up and runs fine…..no going into sleep mode.

A few points:

I wanted to replace the power supply because the Imac was completely shutting down at times, for no reason. It never went into sleep mode, it would shut off and come back up with a message about an unexpected shutdown.

With the new power supply, I noticed the fans ramping up in speed shortly after the imac powered on. This is unusually for this machine, the fans would only come on if the computer was in a heavy load condition and on for an extended time. With the old power supply reinstalled, the fans still have not come on (on for about 30 minutes so far).

Is this a bad power supply from Ifixit? The image from the website matched my power supply, I confirmed it looekd the same before I hit purchase. The one received does look different than mine….so it is different than the image on the website.

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1 Answer

Go into Your preferences > Desktop and Screen Saver settings, click on Screen Saver section then go to the bottom What have you selected for your Start after setting? and your Hot Corners settings? I bet you’ve got them messed up. If not reset your SMC & NVRAM.

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The mac does not go to sleep with the original power supply, no setting changes.

The fact that the fans immediately ramp up to full speed is telling me there is an issue with this power supply.

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@dannyboy454 - Did you run the onboard diagnostics? Restart your system and press the D key to enter, did you get any errors?

Your power supply wouldn't respond like this, something else is messing you up.

Reference: Mac startup key combinations

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