Q. The other day, my Mac laptop would not turn on when I pressed the power button, but a technician was able to get it to start by holding down a bunch of keys. What is this fix?
A. If a Mac does not respond to its power button after you have checked its battery, connections and monitor, there might be a serious issue — but not always. In this case, the computer’s original failure to react when you pressed the power button was most likely a symptom of an issue with the System Management Controller (S.M.C.), a microcontroller on the computer’s logic board that handles various power, light and sensor functions for Macs with Intel processors.
Holding down the Shift, Control and Option keys while pressing down on the power button (or Touch ID button) for at least 10 seconds is a shortcut for resetting the S.M.C. on MacBooks with sealed batteries. If this was the case, the laptop starts up normally again when you press the power button again.
An S.M.C. reset may help if you notice things like the battery is not charging properly, the Mac does not recognize devices plugged into its USB-C port, the keyboard backlight is not working correctly or the sleep function is out of whack. Other symptoms include the computer fan’s running at high speed or the Mac’s acting sluggish, even if you are not using a lot of processor-hogging programs.
Apple’s support site has a full guide to the S.M.C. reset process for all its Intel-based Macs, including those with removable batteries and desktop models. The guide also lists a series of things you should try before resetting the S.M.C. While performing a reset does not generate an alert box or notification, you can tell if you were successful if the odd Mac behavior stops. (You may also have to redo any preferences for your display and power-management settings.)
Resetting the S.M.C. might fix erratic Mac behavior, although it will not help with a damaged power supply or another major hardware problem.
Modern Macs also store some settings in an area of the system called the nonvolatile random access memory (NVRAM); older Macs use parameter random-access memory (PRAM) in a similar manner. If the Mac is not maintaining its settings for volume level, display resolution, time-zone information or preferred start-up disk, information held in the NVRAM may have become corrupt.
You can reset the NVRAM or PRAM by shutting down the Mac and then starting it up again while holding down the Option, Command, P and R keys all at once. When you hear the second start-up tone (or, on a Mac Pro, see a second Apple logo appear and disappear), you can release the keys and let the computer finish its start-up sequence.
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