The Power Management Unit (PMU) is an integrated circuit (computer chip) typically found on a computer's logic board. As its name implies, the PMU is responsible for managing all aspects of the computer's power. It controls hard disk spin down, sleep and wake, some charging aspects, and how any devices attached to the computer affect sleep.
If the settings in the PMU become corrupted, it can result in operational anomalies such as your computer not turning on, not displaying video, or not waking from sleep, among other things. In these situations, you may need to reset your computer's PMU.
Resetting the PMU will not resolve issues in which the computer stalls or is unresponsive. A PMU reset should only be used as a last resort in the case of a hardware failure or when the power management system is suspected. Resetting the PMU returns the computer hardware, including NVRAM, to default settings and forces the computer to shut down.
When to reset the PMU
Before you reset the PMU, try restarting your computer instead, which may resolve your issue. If your computer has stopped responding, try these steps:
- Force Quit (Option-Command-Escape)
- Restart (Control-Command-Power)
- Force Shut Down (press the power button for 10 seconds)
If none of the above steps resolved the situation, reset the PMU.
Reset the PMU
- Unplug all cables from the computer, including the power cord.
- Wait 10 seconds.
- Plug in the power cord while simultaneously pressing and holding the power button on the back of the computer.
- Let go of the power button.
- Press the power button once more to start up your Mac mini.
Important: This procedure also resets the computer's PRAM. Be sure to reset your computer's time, date, and other system parameter settings as necessary.
If you have reset the PMU on a Mac mini and it still isn't displaying video or turning on, contact Apple technical support (1-800-APL-CARE in the U.S.) or schedule a service appointment with either an Apple Retail Store or an Apple Authorized Service Provider.