Apple Xserve G5 - Manual (Page 77)

Xserve G5 Troubleshooting - 3 General Information
Resetting the PMU on the Logic Board
The PMU (Power Management Unit) is a microcontroller chip that controls all power
functions for the server. The PMU is a computer within a computer. Its function is to:
• tell the server 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 logic board. The PMU is very sensitive and
touching the circuitry on the logic board can cause the PMU to crash. If the PMU crashes
and is not reset, the battery life goes from about five years to about two days.
Note: For the location of the PMU reset button, see “Logic Board” in the Views chapter.
Many system problems can be resolved by resetting the PMU chip. When you have a
server that fails to power up, follow this procedure before replacing any modules:
1. Disconnect the power cord and check the battery in the battery holder. The battery
should read 3.3 to 3.7 volts. If the battery is bad, replace it, wait ten seconds, and then
proceed to step 2. If the battery is good, go directly to step 2.
2. Press the PMU reset button once and then proceed to step 3. Do not press the PMU
reset button a second time because it could crash the PMU chip.
3. Wait ten seconds before connecting the power cord and powering on the server. If the
server powers on, go to step 4. If the server does not power on, there is something
else wrong with it; refer to the “Startup” section of “Symptom Charts” in this chapter.
4. Run Xserve Remote Diagnostics to verify the system.
Note: The above procedure resets the server’s PRAM. After resetting the PMU, be sure to
reset the time, date, and other system parameter settings.