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

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CPU fan displays 0 speed after replacment

I just replaced my iMac 2011 21.5 CPU fan since it was reported to have an error

4MOT/4/40000002: CPU-0

After replacing the fan, it still shows 0 speed and still is reported as the same error as above after running the Apple Hardware Test.

Is there anyway I can test the fan to see if it is working on another fan connection in the iMac with the display off?

Thank

Answered! View the answer I have this problem too

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Fans are very simple and they hardly go bad..if it reports the same error with two different fans it’s very unlikely they are both malfunctioning. Probably you have a problem with a resistor on the logic board causing the error.

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Thanks arbaman.

Any details on what resistor to check?

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@dream77 I can't tell for sure as I just deal on portable devices, but iMacs circuits are quite similar. You should have one 5v voltage line and two other lines for speed and management. Since you have no speed at all you have just two left. You'll have to get schematics and a boardview and check the relevant components/lines are within range.

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