Narcoleptic MacBook randomly sleeping? Try an SMC Reset

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Written by Digital Surgeons,
• 6 min read

A few months ago our resident Streetfighter champion and apple snob craig was having issues with his Rev.A MacBook which refused to power on. When it would power on it would randomly decide to power itself off. Being an old school, hardcore, mac guy he immediately thought of doing a PMU (Power Management Unit) Reset. A PMU Reset is something we used to have to do in situations like this to our PowerPC Macs. In PowerPC Macs the Power Manager was a chip that was usually on the logic board. As the name implies, it was responsible for power management of the computer. It controlled backlighting, hard disk spin down, sleep and wake, some charging aspects, trackpad control, and some input/output related to the computer sleeping/waking.

So being the awesome Mac fanboy he is he decided to contribute this article on how to perform an SMC reset to your Macbook.

On Intel machines like my Macbook, there is no PMU but I discovered that there is something that is ALMOST identical in functionality called the SMC. Now, I’m going to show you how to reset your Intel Based Mac’s SMC.

The SMC (System Management Controller) is a chip on the logic board that controls all power functions for your computer, it is responsible for many low-level functions on Intel-based Macs. Some of the functions that are handled by the SMC are:

  • Responding to presses of the power button
  • Responding to display lid opening and closing on portable Macs
  • Battery management
  • Thermal management
  • The SMS (Sudden Motion Sensor)
  • Ambient light sensing
  • Keyboard backlighting
  • Status Indicator Light (SIL) management
  • Battery status indicator lights
  • Selecting an external (instead of internal) video source for some iMac displays

Like I said, it’s almost identical to PMU. When you reset the PMU on a PowerPC it would also reset the PRAM (Parameter RAM) and NVRAM (Non-Volatile RAM) automatically. On Intel Macs, an SMC reset will only reset the SMC firmware back to factory settings, but will not reset the PRAM at the same time (NVRAM is not present on Intel Macs as they are not Open Firmware-based). This means that you’ll have to reset the PRAM on your own when resetting the SMC. I’ll describe that very simple process later on. Ok, so now that we know what the SMC is, how it differs from PMU, and that I’m a pretty big nerd for knowing all of this; lets get into when to reset your SMC and how to do it.

You should consider resetting your SMC firmware if you experience any of the following symptoms:

The computer’s fans speed up quickly and remain at high speed.
The computer’s fans run at high speed although the computer is not experiencing heavy usage and is properly ventilated.

The keyboard backlight appears to behave incorrectly (on Mac computers that have this feature).
The Status Indicator Light (SIL) appears to behave incorrectly (on Mac computers that have an SIL).
Battery indicator lights, if present, appear to behave incorrectly (on portables that use non-removable batteries).
The display backlight doesn’t respond correctly to ambient light changes on Mac computers that have this feature.

The computer doesn’t respond to the power button when pressed.
A portable Mac doesn’t appear to respond properly when you close or open the lid.
The computer sleeps or shuts down unexpectedly.
The battery does not appear to be charging properly.
The MagSafe power adaptor LED doesn’t appear to indicate the correct activity.

System Performance
The computer is running unusually slowly although it is not experiencing abnormally high CPU utilization.

A computer that supports target display mode does not switch into or out of target display mode as expected.
A computer that supports target display mode switches into or out of target display mode at unexpected times.

Ok, so my symptoms were that my computer was sleeping/shutting down unexpectedly and not responding to me pressing the power button. An SMC reset was definitely warranted. Here’s how you do it.

  1. Shut down the computer.
  2. Disconnect the MagSafe power adapter from the computer, if it’s connected.
  3. Remove the battery.
  4. Press and hold the power button for 5 seconds.
  5. Release the power button.
  6. Reconnect the battery and MagSafe power adapter.
  7. Press the power button to turn on the computer.

I no longer have a MacBook with a removable battery, if you purchased your MacBook or MacBook Pro recently (2009 or later MacBook Pro, MacBook Air, and the new MacBook), your machine may not have a removable battery either. The steps are different for those… which was super confusing when I had to do this recently to troubleshoot my new MacBook Pro. Here is how to reset SMC on a Mac notebook without a removable battery.

  1. Shut down the computer.
  2. Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
  3. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
  4. Release all the keys and the power button at the same time.
  5. Press the power button to turn on the computer. Note: The LED on the MagSafe power adapter does not change states or temporarily turn-off when you reset the SMC.

If you’re too cool for school, or a Mac notebook, you can reset SMC on your desktop Mac by performing the following:

  1. Shut down the computer.
  2. Unplug the computer’s power cord.
  3. Press and hold the power button for 5 seconds.
  4. Release the power button.
  5. Attach the computers power cable.
  6. Press the power button to turn on the computer.

And there you have it. You have reset your computer’s SMC. If your machine is still experiencing the symptoms listed above, you likely have a hardware issue and should bring your machine into an Apple Store or some other Mac Specialist to get looked at/repaired. After you reset your SMC its advisable to also reset your Parameter RAM (PRAM). This is super-simple to do.

With your Mac powered off press and hold ⌘ (Command) + Option + P (key) + R (key), then press and hold the power button. You will hear the startup chime, keep all of the buttons pressed (including the power button) until the startup chime sounds 3 or more times, then release. Your mac will boot up and your PRAM will be reset.