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How to reset portable Macs power management units Laptop Macs
The keyboard and trackpad completely failed on a friend's MacBook Pro Intel Core 2 Duo 15.4" running OS 10.4. According to Apple tech support, this had something to do with power management, and he gave this procedure to restore functionality, which worked:
  • Remove battery and power adapter.
  • Hold down power button for 10 seconds.
  • Reinstall battery and attach power adapter.
  • Hold down Command-Option-P-R, a total of four keys, and press power button. Don't release the keys.
  • Continue holding the four keys until you hear the startup sound twice, then release.
After doing this, the machine should then boot up with normal function.

[robg adds: To be completely precise, MacBooks and MacBook Pros manage ppower through the System Management Controller (SMC), and here are Apple's official reset instructions for those machines. For PowerPC portables, power was managed by the Power Management Unit (PMU), and here are those reset instructions. As noted in both articles, resetting the SMC/PMU should always be the fix of last resort.]
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How to reset portable Macs power management units
Authored by: dhjdhj on Feb 22, '07 02:18:20AM

I'm a little baffled - exactly what purpose is served by holding the power button down for 10 seconds if there is neither power nor battery?

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How to reset portable Macs power management units
Authored by: Anonymous on Feb 22, '07 03:34:17AM

there is another battery in a computer so even when no power is going to machine......the holding down of power button for 10 seconds leads to a reset of the PMU......hope you are not still baffled

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