User Guide

10 - Mac mini Troubleshooting
Reset the PMU
Reset the PMU
How to Reset the PMU
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.
Before you reset the PMU, try restarting the computer instead, which may resolve the
issue. If the computer has stopped responding, try these steps, in order, until the computer
responds:
• 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 with the Top Housing On
1. Unplug all cables from the computer, including the power cord.
2. Wait 10 seconds.
3. Plug in the power cord while simultaneously pressing and holding the power button on
the back of the computer.
4. Let go of the power button. Your computer should start up.
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 none of the above steps resolved the situation, reset the PMU. Follow the procedures on
the next page.