PowerBook, Resetting Power Management Unit (PMU)

If you press the power button on your Mac portable and it fails to power up, it can be due to a misbehaving Power Management Unit (PMU). One of the self-help remedies is to reset the PMU and in most models of Mac portables from the iBook G3 line onwards, this can be done simply by pressing a key combination at startup.

If this prescribed remedy doesn’t help then its best you bring your Mac portable down to your local Apple Service Provider without delay.

Other reasons for failing to power up, could be:

  • a faulty power switch/button;
  • a bad DC board;
  • a bad logic board;
  • all of the above

To reset the PMU — Press CTRL + Option + Shift + your Mac’s power button simultaneously.

This is also a recommended solution if you find that your Mac’s battery life may not be as advertised or declining over a period of time. Bearing in mind that you may not observe phenomenal increases in battery life but at times, a slight increase may be observed.

This is also recommended, if you have recently updated your 15″ Aluminium Powerbook with Apple’s, Aluminum PowerBook (15-inch) Battery Update 1.0.

Note: resetting the PMU may affect your date and time settings and requires re-calibration during your first start-up after committing the PMU reset.

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