Question about Apple PowerMac G5 Dual Mac Desktop

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Fans don't run

G5 dual 1.85Ghz desktop. Yesterday fan on top level (between optical drive and hard drives) began running loudly and a red light came on inside, located just above on switch. Opened it up - no dust buildup. Closed it back up, restarted. Now the red light doesn't come on and there is no loud fan noise - but apparently NONE of the fans are coming on.

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Thank you for the complete and literate problem statement.
The red light in question will come on and the media bay fan will spin at high speed if the plastic air deflector door is not in place, OR the white sensor label on the lower right tab of the air deflector door is damaged or out of position, OR the air deflector sensor board is faulty.
You can differentiate a bad sensor label from a bad sensor board by doing the following: Remove the air deflector door. Slide a folded piece of paper through the slot in the enclosure where the right tab of the air deflector would normally be inserted. If the red LED goes out (but stays on with the door in place), the sensor label on the door is missing or damaged.

You will also want to check the sensor board cable connection on the logic board (second from right connector located directly below the hard drives).

Subsequent failure for the fans to run does not necessarily indicate a problem, as the fans are temperature-controlled and will not run until heat rises to a certain level. If the fans are not coming on even when the heat is sufficient, you may need to reset the SMU by shutting down the computer, unplugging the AC cord, waiting 15 seconds, and then replugging and restarting the computer.

Posted on May 17, 2010


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