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Troubleshooting General/ Logic Board Troubleshooting - 11
I/O, two crystals, and a CPU. Its function is to:
• Tell the computer to turn on, turn off, sleep, wake, idle, etc.
• Manage system resets from various commands.
• Maintain parameter RAM (PRAM).
• Manage the real-time clock.
Important:
Be
very
careful when handling the main logic board.
Remove the battery when handling the logic board so the PMU is
not affected. The PMU is
very
sensitive and touching the circuitry
on the logic board can cause the PMU to crash. If the PMU crashes,
the battery life goes from about five years to about two days if the
PMU is not reset. The PMU chip is located on the underside of the
logic board at U20; refer to the Power Mac G4 (AGP Graphics/
Gigabit Ethernet/Digital Audio) Logic Board Diagrams for the
location of the PMU button.
Many system problems can be resolved by resetting the PMU chip.
Whenever you have a unit that fails to power up, follow this