Fan not detected Mid 2010 27" iMac

Question

Level 1

22 points

Fan not detected Mid 2010 27" iMac

Just replaced a defective GPU on my mid-2010 iMac and also decided to replace the factory hard drive with an SSD (using OWC kit) while I had the computer open.

Upon reassembly the display worked again, the overall speed was way faster thanks to the SSD...and the CPU fan was no longer detected. The fan was blowing at full speed, obviously not having failed but simply not detected and therefore running at maximum.

I bought another CPU fan from a recycler on eBay and that fan is now doing the exact same thing. It seems the problem was not the fan but perhaps the controller on the motherboard that interfaces with the fan.

The fan noise at full speed is horribly loud but my bigger concern is that it will burn out quickly running at maximum and then cause the CPU to overheat.

Does anyone have a solution to make this right? I know that a 10 year old computer is considered obsolete but apart from the fan this iMac is working beautifully and I'd like to keep it in service.

iMac Line (2012 and Later)

Posted on Oct 9, 2020 12:20 PM

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Answer 1

BDAqua

Level 10

250,259 points

Oct 9, 2020 1:30 PM in response to LeifD

My 3 fans have been running near full speed for years.

1.. Shut the machine down.

2.. UNPLUG the power lead to the computer and any peripheral devices.

3.. leave it for 10 minutes.

4.. Hold power Button in for 10 seconds

5.. Connect everything back up and restart.

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Answer 2

den.thed

Level 10

92,614 points

Oct 9, 2020 1:26 PM in response to LeifD

Ah’ I was looking at your screen shot and thought that fan was not running at all.

That connector could also be why the fan is not reporting the correct rpm back to the System Management Controller.

Can you use that temp software to control the fan speed? If so, try setting the speed at somewhere around 2600 to 2800 rpm and see if the fan responds. If not then uninstall that software, reset the SMC and try using MacFanControl.

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Answer 3

rkaufmann87

Level 10

148,606 points

Oct 9, 2020 12:24 PM in response to LeifD

OWC sells a cable that is to be used when users remove the original drive and upgrade to another HD or SSD. I suspect you did not buy their install kit with the tools as the cable would have been included.

You can still buy it or you can download some fan control software.

The fan sensor was integrated into the original HD beginning in 2009, when you upgrade that sensor is not present in almost all third party upgrades.

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Answer 4

den.thed

Level 10

92,614 points

Oct 9, 2020 12:45 PM in response to LeifD

Because you tried another fan. I would look real hard at the fan connector socket on the logic board to see if is damaged or if the little connector pins are bent or missing.

I would also be very careful not to cook the CPU and GPU until the fan issue is resolved.

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Answer 5

Zahilla

Level 2

270 points

Oct 10, 2020 11:23 AM in response to LeifD

I had a problem like this on a 2007 24’ iMac and I replaced the fan three times so what I had to do was replace the logic board to fix it and transfer the cpu gpu and ram

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Answer 6

LeifD Author

Level 1

22 points

Oct 9, 2020 1:46 PM in response to BDAqua

BDAqua wrote:

1.. Shut the machine down.

2.. UNPLUG the power lead to the computer and any peripheral devices.

3.. leave it for 10 minutes.

4.. Hold power Button in for 10 seconds

5.. Connect everything back up and restart.

Same :(

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Answer 7

rkaufmann87

Level 10

148,606 points

Oct 9, 2020 12:37 PM in response to LeifD

Well when working on antiques (sorry to say your 2010 really is an old computer now) you never know what issues you may run into. The only thing I can thing of is possibly when you re-assembled a cable was not connected or may have broken. These cables get brittle with age and on an 11 year old computer your cables may be pretty brittle.

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Answer 8

LeifD Author

Level 1

22 points

Oct 9, 2020 12:29 PM in response to rkaufmann87

I used the OWC kit that included their special cable. I'm familiar with that problem but that doesn't seem to be the cause.

Also I explored the idea of using fan control software but that's not an option if the fan isn't detected in the first place. (see screenshot from original post.)

Other thoughts?

Thanks.

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Answer 9

LeifD Author

Level 1

22 points

Oct 9, 2020 1:11 PM in response to den.thed

Thanks for the tip. I just checked the pins on the logic board connector and they are fine.

CPU and GPU won't get cooked since the fan is running full speed; the problem is that the fan will fail because of this and then the CPU gets cooked for sure.

Back to the drawing board.

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Answer 10

LeifD Author

Level 1

22 points

Oct 9, 2020 1:49 PM in response to den.thed

den.thed wrote:

Ah’ I was looking at your screen shot and thought that fan was not running at all.

That connector could also be why the fan is not reporting the correct rpm back to the System Management Controller.

Can you use that temp software to control the fan speed? If so, try setting the speed at somewhere around 2600 to 2800 rpm and see if the fan responds. If not then uninstall that software, reset the SMC and try using MacFanControl.

This is actually the second app I've used to try and control the fans. It appears that the problem is not being able to communicate with the fan at all, though it does have power & runs at full speed.

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