Model A1311 / Late 2009 / 3.06 or 3.33 GHz Core 2 Duo processor

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Fan running in full speed

Originally, my Imac had an internal sound problem. When playing music, video or whatever that requires the sound system to work, the internal speaker emitted something like alien talk. The technician came to replace the logic board, but then the fan is running in full speed. Now the old logic board is re-used, the sound problem disappeared but the fan is still running in full speed.

Now the technician need to take back my Imac and I hesitate.

I want to open my Imac, is there anything I can check?

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If one of these answers fixed your problem please hit the "accept" in list that has "History Edit Flag Accept Comment" located to the upper right of your question so we can remove it from the unanswered list. Thanks so much.

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Yes there is...I imagine that you reset the SMC or System Management Controller by Shutting down and unplugging all of the Cables, including the power cord.. you need to wait at least 15 seconds, the reset occur's automatically once the Imac has been disconnected from the Power Source.. if this does not take care of the High Speed Fan Issue It sounds like the Tech did not plug in one of 6 Sensor's or one of them was not properly attached and came loose

Power Supply

ODD Temperature

Ambient Temperature

LCD Temperature

GPU Temperature

CPU Temperature

All of these will cause the Fan's to run at Full Speed...

If you feel like taking the Cover's and Display off, you could look around to see if one of them came unplugged from the Logicboard.

You could carefully follow the take-apart and nose around a bit.. but be careful and Safe.

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Thank you for your response,

I did the SMC reset several times, and tried to examine the inside myself. It seems that all cables are properly attached. I took it back to the repair center, the noise is unbearable. But a little bit disappointed.

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unplugging for 30 seconds worked thanks so much!!!

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Check your iMac's firmware ... I have rebooted and made sure firmware was installed before boot process

sequence. Had a similar issue happen also but once the firmware was installed the problem had stopped.

Do not just think that resetting SMC is a cure all solution, although it is a good starting point.

I would double check your issue by rebooting your iMac in safe (boot) mode .. then you will know for sure.

Instructions on safe boot mode can be found via the net same with install of new firmware. If problems persist .. must be escalated to a problem w/ motherboard and/or replacement.. Call AppleCare if your are still under warranty. Best of Luck

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I have a similar problem but for a different reason.

I have a 21 inch Imac and i recently changed the 500g HD for a 1G.

In the procedure it noted to be aware of the fan control connector position on the HD, and that installing reverse would cause it to run on high. I think i read it wrong however.....i put it back in the original orientation and now my fan is on high all the time.

Does it make sense to have to reverse the fan cable orientation when changing drives?

OR - am i missing the point all together....i am thinking the thermal sensor is the 4 pin connector on the hard drive next to the sata and power connectors? Are there versions of drives out there where there are more than 4 pins?

Cheers

Mac

Step 10 — Hard Drive ¶

Before disconnecting the thermal sensor cable, take note of its orientation. It is extremely important to reinstall the connector reversed from the current orientation so the fans will not run at full speed.

Disconnect the thermal sensor by pulling its connector away from the side of the hard drive.

During reassembly, be sure that the thermal sensor connector is connected to set of pins closest to the SATA connectors. If the fans spin at full speed, reverse the connector's position

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Robert will be eternally grateful.
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