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Model A1312 / Mid 2010 / 3.2 GHz Core i3 or 2.8 & 3.6 GHz Core i5 or 2.93 GHz Core i7, ID iMac11,3

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Problems after replacing PSU

My EMC 2390 (mid-2010 27”) iMac had a dead PSU. After replacing the PSU with one from iFixit, firstly the fans go crazy (I know have to use Macs Fan Control which I didn’t before) but most annoyingly the iMac’s display blacks out, then the iMac goes to sleep, after about 30 seconds. I read a comment from another poster who had the exact same issue and advised resetting the NVRAM on boot - this works for me as well, but like that poster I have to do it every time I boot or else the problem reoccurs. I’ve tried resetting SMC also with no improvement.

I am thinking it’s something wrong with the iFixit PSU, but not sure. Would appreciate any guidance!

Edit: added screenshot of TG Pro

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Restart your system and press the D key to enter into the onboard diagnostics, did you get any errors? Let us know what you got.

Reference: Mac startup key combinations


@danj thanks for your response!

Couldn't run Diagnostics - doesn't appear to be on my machine - but was able to run Apple Hardware Test via a bootable USB.

Only one error - 4M0T/4/40000003: HDD-1314 which looks like an issue with the HDD fan? I no longer have a HDD, replaced with a SSD a couple of years ago. HDD fan is not the one that is going crazy - it's the CPU fan.


Whennyou changed the hard drive, did you do anything to take care of the thermal sensor?


@mayer I added the OWC In-line Digital Thermal Sensor Cable when I changed the HDD to SSD. I did that change 4 years ago, and the iMac has run with no issues until I replaced the PSU. Now I have the iMac going to sleep and the CPU fan running crazy.


I am having the same issue after replacying the PSU of my iMac 27 Mittel 2011.

After few (many) reboots iMac runs smoothly.

The issue occurs always when I turn the iMac on for the first time.


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Thats the problem as SMC is seeing the fan has failed so its pushing the other fans to make sure your system doesn’t cook.

While a SSD runs much cooler than a older 3.5” HDD you’ll still need to replace the fan iMac Intel 27" (Late 2009-Mid 2011) Hard Drive Fan. We don’t have a direct guide to get to it as its under the logic board.

Update (10/20/2021)

OK, did you install the sensor as shown in Step 19 iMac Intel 27" EMC 2390 Hard Drive Replacement

Also check your connections to the logic board

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iMac Intel 27" (Late 2009-Mid 2011) Hard Drive Fan Afbeelding


iMac Intel 27" (Late 2009-Mid 2011) Hard Drive Fan


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Thanks @danj! That makes sense and somewhat explains the fan speed issue, although I can actually control the HDD fan no problem with Macs Fan Control, so not sure the fan has fully failed.

My bigger concern is the entire iMac going to sleep after about 30 seconds, unless I reset the NVRAM on boot? Any suggestions or troubleshooting steps on why that is happening?


@Graeme Lobley - I would replace the fan, software doesn't overcome the SMC error condition, only slow the fan down. The shutdown is likely cause by SMC sensing an over heating problem.

Lets do this, get this software installed TG Pro You'll likely need to contact them to get the version your older OS-X needs contact:

Take a snapshot of the main window so we can see all of the sensors and fans (not running any software to alter them) and post it here for us to see Voeg afbeeldingen toe aan een bestaande vraag


@danj thanks - I have downloaded TG Pro and attached the screenshot requested to the original post.


@Graeme Lobley - It appears the fan is not connected! Which is why TG Pro has it as an error condition as well (not listed).

Time to replace the fan


@danj what are you are seeing that indicates the fan is not connected? All three fans are running (rpm is changing). The ODD fan is running just below 1000 rpm so doesn't show up on the indicator. The HDD fan is showing ~1600 rpm and the CPU fan is running full blast.


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Graeme Lobley zal eeuwig dankbaar zijn.

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