Mac Repair Central

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 off, 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 suffice. If the computer isn't responding, perform these steps one at a time, in the following order, until the issue has been resolved:

1. Force Quit (Option-Command-Escape)
2. Restart (Control-Command-Power)
3. Force Shut Down (press the power button for 10 seconds)

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 (8x).

You can use the SMC reset switch:

1. From the Apple menu, choose Shut Down (or if the computer is not responding, hold the power button until it turns off).
2. Press the SMC_RST switch, which is located to the right and slightly below the row of 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).
3. Press the power button to start up the computer. Or, you can reset the SMC by removing AC power:
4. From the Apple menu, choose Shut Down (or if the computer is not responding, hold the power button until it turns off).
5. Unplug the AC power cord.
6. Wait at least 15 seconds.
7. Plug the power cord back in, making sure the power button is not being pressed at the time.
8. Press the power button to start up the computer.

Real Time Clock (RTC) Reset

The Real Time Clock (RTC) is a chip on the logic board that controls the date and time functions of the computer. If the computer is experiencing an issue booting, resetting the RTC may resolve it. Follow these steps to reset the RTC:

1. From the Apple menu, choose Shut Down (or if the computer is not responding, hold the power button until it turns off).
2. Unplug the AC power cord.
3. Remove the battery for at least 20 seconds. You may need to remove a PCI Express card to have access to the battery.

System Reset

Mac Pro (8x) has a system reset switch on the logic board that may be used to restart the system while it is powered up. This switch can be used to determine if a computer that won't consistently boot from a cold start has power supply issues. Follow these steps to reset the system:

1. With the computer powered up, press the SYS_RST switch located in the upper right-hand corner of the logic board. To press the switch, use the nylon probe tool (Apple part number 922-5065).
2. If the computer boots after you press the SYS_RST switch, try shutting the computer off and restarting by pressing the front power button. If the computer restarts when you press the SYS_RST switch but not from a cold start, the power supply may need to be replaced.

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