How to reset the SMU on a Power Mac G5 (Late 2004) or Power Mac G5 (Late 2005)

How to reset the SMU on a Power Mac G5 (Late 2004) or Power Mac G5 (Late 2005)
Last Modified on: July 17, 2006
Article: 300341
Learn how to reset the SMU on Power Mac G5 (Late 2004) and Power Mac G5 (Late 2005) computers, and when to do so.

The SMU (System Management Unit) is a microcontroller chip on the logic board that controls all power functions for your computer. If your computer is experiencing any issues regarding these functions, resetting the SMU may resolve the issue. The functions controlled by the SMU include:

It tells the computer when to turn on, turn off, sleep, wake, idle, and so on.
It handles system resets from various commands.
It controls the fan.
Note that resetting the SMU does not reset the PRAM.

Resetting the SMU will not resolve issues in which your computer is unresponsive--in these situations, restarting your computer will generally suffice. If your computer isn't responding, perform these steps one at a time, in this order, until the issue has been resolved:

Force Quit (Option-Command-Escape)
Restart (Control-Command-Power)
Force Shut Down (press the power button for 10 seconds)
Resetting the SMU can resolve some computer issues such as not starting up, not displaying video, sleep issues, fan noise issues, and so on. If your computer still exhibits these types of issues even after you've restarted the computer, try resetting the SMU.

Power Mac G5 (Late 2004)
To reset the SMU on a Power Mac G5 (Late 2004) computer, simply do the following:

Turn off the computer by selecting Shut Down from the Apple menu or by holding the power button until the computer turns off.
Remove the power cord from the computer.
Wait two minutes.
Plug in the power cord.
Turn on the computer.
Power Mac G5 (Late 2005)
To reset the SMU on a Power Mac G5 (Late 2005) computer, either use the steps listed above for the Power Mac G5 (Late 2004) or:

Turn off the computer by selecting Shut Down from the Apple menu or by holding the power button until the computer turns off.
Open and remove both the metallic outer door and the inner plastic air deflector.
Remove the fan assembly immediately to the left of the processor module.
Press the SMU reset button on the logic board.
Replace the fan assembly, air deflector, and outer door.
Turn on the computer.
The SMU reset button is located underneath the lower bank of system memory slots, as shown below:


Unlike earlier models of Power Mac G5 or Power Mac G4 computers, the Power Mac G5 (Late 2004) and (Late 2005) models do not have a PMU. This functionality has been replaced by the SMU.