Apple emac ati usb2 2005 Service Manual
eMac ATI Graphics /USB 2.0/2005 Troubleshooting -
13
General Information
The PMU Chip
The PMU (Power Management Unit) is a micro controller chip that controls all power functions
for the computer. The PMU is a computer within a computer. It has memory, software, firmware,
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.
for the computer. The PMU is a computer within a computer. It has memory, software, firmware,
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:
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. Refer to the next topic, “How to Reset the PMU on the Logic Board” for the
procedure.
the PMU is not reset. Refer to the next topic, “How to Reset the PMU on the Logic Board” for the
procedure.
Many system problems can be resolved by resetting the PMU chip. The PMU reset button is located
behind the user access door, refer to the graphic below.
behind the user access door, refer to the graphic below.
Location of the PMU Reset Button on the eMac (ATI Graphics)