User Guide

Mac Pro Troubleshooting — General Information 145
Resetting the Logic Board
System Management Controller (SMC) Reset
The System Management Controller (SMC) is a chip on the logic board that controls all power
functions for the computer. If the computer is experiencing any power issue, resetting the SMC
may resolve it. The SMC controls several functions, including:
Telling the computer when to turn on, turn o, sleep, wake, idle, and so forth•
Handling system resets from various commands•
Controlling the fans•
It is also recommended that the SMC be reset after a logic board, ambient board, or ambient
board cable is replaced as part of a repair.
Note that resetting the SMC does not reset the PRAM. Resetting the SMC will not resolve issues in
which the computer is unresponsive—in these situations, restarting the computer will generally
suce. If the computer isn’t responding, perform these steps one at a time, in the following order,
until the issue has been resolved:
Force Quit (Option-Command-Escape)1.
Restart (Control-Command-Power)2.
Force Shut Down (press the power button for 10 seconds)3.
Resetting the SMC can resolve some computer issues such as not starting up, not displaying
video, sleep issues, fan noise issues, and so forth. If the computer still exhibits these types of
issues after you’ve restarted the computer, try resetting the SMC. There are two ways to reset the
SMC on Mac Pro.
You can use the SMC reset switch:
From the Apple menu, choose Shut Down (or if the computer is not responding, hold the 1.
power button until it turns o).
Press the SMC_RST switch, which is located to the right and slightly below the row of 2.
diagnostic LEDs. (See the LED diagram in the following “Diagnostic LEDs” section.) To press
the switch, use the nylon probe tool (Apple part number 922-5065).
Press the power button to start up the computer.3.
Or, you can reset the SMC by removing AC power:
From the Apple menu, choose Shut Down (or if the computer is not responding, hold the 1.
power button until it turns o).
Unplug the AC power cord.2.
Wait at least 15 seconds.3.
Plug the power cord back in, making sure the power button is not being pressed at the time. 4.
Press the power button to start up the computer.5.