Resetting the PMU on the Logic Board

Resetting the PMU (Power Management Unit) on the logic board can resolve many system problems. Whenever you have a unit that fails to power up, you should follow this procedure before replacing any modules.

  1. Save open documents and quit all open applications.
  2. Turn the computer off by choosing Shut Down from the Special menu (if using Mac OS 9), or choose Shut Down from the Apple menu if using OS X.
  3. Unplug all cables, except the power cord, from the computer.

4. Place the computer face down on an ESD matt or soft cloth. Remove the user access door screw.

5 Touch the metal surface inside the computer. Then unplug the power cord.This helps protect the computer from damage caused by electrostatic discharge. Important: To avoid electrostatic discharge, always ground yourself by touching metal before you touch any parts or install components inside the computer. To avoid generating static electricity, do not walk around the room until you have finished the procedure and closed the computer.

6 Press the PMU reset button (shown below) once and then proceed to step 7. Do NOT press the PMU reset button a second time because it could crash the PMU chip.

Pmu Reset Emac

7 WAIT ten seconds before connecting the power cord and powering the computer on. If the computer powers on, go to the next step. If the computer does not power on, there is something else wrong with the computer, refer to the symptom/cure, "No Power" in this chapter.

8 Run diagnostics, either MacTest Pro (for Mac OS 9 booting systems) or Apple Service Diagnostics (for Mac OS X booting systems) and then return the computer to the customer.

Note: This entire procedure resets the computer's PRAM. Be sure to reset the computer's time, date and other system parameter settings before returning the computer to the customer.

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DIY Battery Repair

DIY Battery Repair

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