Reset the System Management Controller (SMC)

bbloke

bbloke

Registered
Apple provide information about how to reset the System Management Controller (SMC) on Intel Macs, when troubleshooting a number of hardware-related issues. I've collected the different instructions, below, to provide a single guide for resetting the SMC on current Macs:

1) Mac Pro

Apple said:
Summary
The System Management Controller (SMC) is a chip on the logic board that controls all power functions for your computer. If your 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.

Products Affected
Mac Pro

Note that resetting the SMC does not reset the PRAM. Resetting the SMC 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:

  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 your computer still exhibits these types of issues after you've restarted the computer, try resetting the SMC.

To reset the SMC on a Mac Pro:

  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 all cables from the computer, including the power cord and any display cables.
  3. Wait at least fifteen seconds.
  4. Plug the power cord back in, making sure the power button is not being pressed at the time. Then reconnect your keyboard and mouse to the computer.
  5. Press the power button to start up your computer.
Another way to reset the SMC on a Mac Pro computer is:

  1. From the Apple menu, choose Shut Down (or if the computer is not responding, hold the power button until it turns off).
  2. Open and remove the metallic outer door.
  3. Press the SMC_RST switch that is located slightly below and to the right of the row of diagnostic LEDs. Use a non-metallic, non-conductive object, such as a wooden pencil. Note: Mac Pro (Early 2008) does not have an SMC_RST switch, refer to the reset procedure steps in the previous section.
  4. Replace the metallic outer door.
  5. Press the power button to start up your computer.

Unlike models of Power Mac G5 or Power Mac G4 computer, the Mac Pro computer does not have a PMU. This functionality has been replaced by the SMC.
Click to expand...



2) iMac and Mac mini
Apple said:
Summary
The System Management Controller (SMC) is a chip on the logic board that controls all power functions for your computer. If your 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.

Products Affected
Mac mini (Early 2006), Mac mini (Late 2006), Mac mini (Mid 2007), iMac (24-inch, Late 2006), iMac (Early 2006 17-inch), iMac (Early 2006 20-inch), iMac (Mid 2006 17-inch), iMac (24-inch Mid 2007), iMac (20-inch, Mid 2007), iMac (17-inch, Late 2006), iMac (17-inch, Late 2006 CD), iMac (20-inch Late 2006)

Note that resetting the SMC does not reset the PRAM. Resetting the SMC 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:

  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 your computer still exhibits these types of issues after you've restarted the computer, try resetting the SMC. To reset the SMC on an iMac (Early 2006), iMac (Mid 2006), iMac (Late 2006), or Mac mini (Early 2006):

  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 all cables from the computer, including the power cord and any display cables.
  3. Wait at least 15 seconds.
  4. Plug the power cord back in, making sure the power button is not being pressed at the time. Then reconnect your keyboard and mouse to the computer.
  5. Press the power button on the back to start up your computer.
The iMac (Early 2006) and later models do not have a button on the main logic board for resetting the SMC, which eliminates the need to remove the computer's cover to reset it (as required for some earlier models).
Click to expand...


3) MacBook, MacBook Pro, and MacBook Air
Apple said:
Summary
Learn more about the MacBook, MacBook Pro and MacBook Air's System Manager and how to reset it.

This article refers to Apple's Intel-based portables manufactured February 2006 or later. For PowerPC-based products manufactured before that date, see "Resetting PowerBook and iBook Power Management Unit (PMU)".

Products Affected
MacBook, MacBook Pro, MacBook Air

The System Management Controller is an integrated circuit (computer chip) that is on the logic board of the computer. As the name implies, it is responsible for power management of the computer. It controls backlighting, hard disk spin down, sleep and wake, some charging aspects, trackpad control, and some input/output as it relates to the computer sleeping.

Over time, the settings in the System Management Controller may become unusable, which can result in operational anomalies with the computer. Examples include not turning on, not waking from sleep, not charging the battery, or not recognizing the AC Adapter, among others.

Resetting the SMC is not intended for resolution of a stall or situation in which the computer is unresponsive. An SMC reset should not be necessary except as a last resort in cases where a hardware failure of the power management system is suspected. Performing an SMC reset returns the hardware, including NVRAM (Non-Volatile Random Access Memory), to default settings and forces the computer to shut down.

For most situations, a restart is sufficient. If the computer has stopped responding, try each one of these steps, one by one. Test in between steps to see if it has worked. If one step works, don't worry about the next, as you're up and running! Only go on to reset the SMC if you've tried all of the steps listed here and the computer still isn't working.

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

Only perform an SMC reset on the computer if none of the above steps resolved the situation. If this is the case, see below for instructions on locating the reset button or key combination for your model of computer. If your computer is earlier than the models listed here, see "Resetting PowerBook and iBook Power Management Unit (PMU)" or "PowerBook: Resetting Power Management Unit (PMU)".

MacBook, MacBook Pro
  1. If the computer is on, turn it off.
  2. Disconnect the AC Adapter and remove the computer's battery.
  3. Press and hold down the power button for 5 seconds and then release the button.
  4. Reconnect the battery and AC Adapter.
  5. Press the Power button to restart the computer.
MacBook Air
  1. If the MacBook Air is on, turn it off.
  2. Connect the power adaptor to a working power source.
  3. On the MacBook Air keyboard, press (left) Shift-Control-Option along with the power button once.
Note: You must use the keys on the left side of the MacBook Air keyboard.
Wait 5 seconds and press the power button to start the MacBook Air.
Apple recommends only performing an SMC reset when the MacBook Air has been properly shutdown. This prevents issues from occurring to the file system.

While the power adaptor does not need to be connected to reset the SMC, it may be necessary in situations where the battery needs charging, or the MacBook Air has been without power for an extended period of time.
Click to expand...


These procedures replace resetting the Power Management Unit (PMU) on PowerPC Macs, such as the PowerBook and iBook.
 
You must log in or register to reply here.
Back
Top