The System Management Unit (SMU) controls various power-related functions on your iMac G5 computer. If you're having problems getting your computer to turn on, wake up from sleep, turn off or run the fan, then it may help to reset the SMU.
Reset the SMU On An IMac G5
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Turn off your computer and wait until it has completely powered down. You shouldn't be able to hear any noise from the fan or processor.
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Unplug the power cord from the electrical outlet or turn off the power strip that the iMac G5 is on. Disconnect the power cord from the back of the computer. If your iMac was made in late 2004, then you just have to wait about 2 minutes with the cord disconnected to reset the SMU.
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Disconnect all the cables from the computer if you have a different or later model iMac G5. Wait about 1 minute and then press and hold the power button while connecting the computer's power cord. The cord should be connected to a power outlet for this step.
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Release the power button after you plug in the power cord. The SMU on the iMac G5 should have been reset, so now you can reconnect the computer and power it on.
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Check the date and time on your computer to see whether the SMU has been reset. If done correctly, your computer should think it is December 31, 1969. You may also have to correct some other settings, such as the mouse scroll speeds and Energy Saver preferences.
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Consider backing up your important files and reinstalling OS X if the SMU reset didn't fix your problems. You may also want to repair the disc permissions with the Disc Utility application.
Tips & Warnings
- Some functions, such as your computer's date and time, will be reset with the SMU but no files will be lost.
- If the SMU reset didn't fix your problems, try reseting the PRAM and NVRAM. Turn on your computer and then immediately press and hold the "Command," "Option," "P" and "R" keys and listen for the startup chime to go off three times. Release the keys after the third chime and the computer should boot normally.
- The SMU reset will often only help problems related to your computer starting up and waking up from sleep mode.
- Always correct the date and time after reseting the SMU. Secure Internet connections and some software requires your computer to be set to the current date.
