MacOS Reset the System Management Controller (SMC) and NVRAM

Check the sources pages for more details and how to do in other versions of MACs

source reset SMC https://support.apple.com/en-ie/HT201295

source reset NVRAM https://support.apple.com/en-ie/HT204063

 

Reset the SMC on Mac notebook computers

reset-smc-macbook-air

First, determine whether the battery is removable. Mac notebook computers that have a nonremovable battery include MacBook Pro (Early 2009) and later, all models of MacBook Air, MacBook (Late 2009), and MacBook (Retina, 12-inch, Early 2015) and later. Learn more about Mac notebook batteries.

If the battery is nonremovable:

  1. Shut down your Mac.
  2. Unplug the MagSafe or USB-C power adapter from your computer.
  3. Using the built-in keyboard, press Shift-Control-Option on the left side of the keyboard, then press the power button at the same time. Hold these keys and the power button for 10 seconds.
  4. Release all keys.
  5. Reconnect the power adapter.
  6. Press the power button again to turn on your Mac.

If the battery is removable:

  1. Shut down your Mac.
  2. Disconnect the MagSafe power adapter from your computer.
  3. Remove the battery. (Learn about removing the battery in MacBook and MacBook Pro computers.)
  4. Press and hold the power button for 5 seconds.
  5. Reconnect the battery and MagSafe power adapter.
  6. Press the power button to turn on your Mac.

The LED on MagSafe power adapters might change colors or temporarily turn off when you reset the SMC.

How to reset NVRAM

pram-reset-graphic

Follow these steps to reset your Mac computer’s NVRAM.

If you have a late-2016 MacBook Pro, the steps are slightly different. Skip to the next section for instructions.

  1. Shut down your Mac.
  2. Find Command (⌘), Option, P, and R on your keyboard.
  3. Turn on your Mac.
  4. Press and hold the Command-Option-P-R keys immediately after you hear the startup sound.
  5. Hold these keys until the computer restarts and you hear the startup sound for a second time.
  6. Release the keys.

After resetting NVRAM, you might need to reconfigure settings for speaker volume, screen resolution, startup disk selection, and time zone information.

If issues related to these features continue on a desktop Mac (like an iMac, Mac mini or Mac Pro), its logic board battery might need to be replaced. The logic board battery on desktop computers helps retain NVRAM settings when your Mac is unplugged. You can take your Mac to an Apple Store or Apple Authorized Service Provider to replace the battery on the logic board.