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iMac G5 (20-inch iSight) Troubleshooting — Symptom Charts 165
Fans are running at a constant high speed
If the fans on the system are running at a constant high speed, or ramp very quickly to high
speed and do not vary once this speed is reached, the fans are most likely receiving incorrect
thermal input. Follow these steps:
Reset the SMU (refer to “Resetting the SMU” mentioned earlier in this chapter) and then test 1.
to see if the fans still exhibit the issue.
Boot to Apple Service Diagnostic v2.5.8 or later Open Firmware (OF) partition and run the 2.
suite of tests. This will test the fans and thermal input of the sensors. If the tests fail, replace
the component (s) indicated by the test.
Verify that the hard drive temperature sensor cable, and the optical drive temperature 3.
sensor cable are plugged in correctly. If necessary, replace the hard drive and optical drive
temperature sensor cables.
Replace the hard drive and optical drive temperature sensors.4.
Replace the hard drive.5.
Replace the logic board.6.