User Guide
Mac Pro Troubleshooting — General Information 146
Real Time Clock (RTC) Reset
The Real Time Clock (RTC) is a chip on the logic board that controls the date and time functions
of the computer. If the computer is experiencing an issue booting, resetting the RTC may resolve
it. Follow these steps to reset the RTC:
From the Apple menu, choose Shut Down (or if the computer is not responding, hold the 1.
power button until it turns o).
Unplug the AC power cord.2.
Remove the battery for at least 20 seconds. You may need to remove a PCI Express card to 3.
have access to the battery.
System Reset
Mac Pro has a system reset switch on the logic board that may be used to restart the system
while it is powered up. This switch can be used to determine if a computer that won’t
consistently boot from a cold start has power supply issues. Follow these steps to reset the
system:
With the computer powered up, press the SYS_RST switch located in the upper right-hand 1.
corner of the logic board. To press the switch, use the nylon probe tool (Apple part number
922-5065).
If the computer boots after you press the SYS_RST switch, try shutting the computer o and 2.
restarting by pressing the front power button. If the computer restarts when you press the
SYS_RST switch but not from a cold start, the power supply may need to be replaced.
Power-On Self Test: RAM and Processor Verication
A power-on self test in the computer’s ROM automatically runs whenever the computer is started
up after being fully shut down (the test does not run if the computer is only restarted). If the test
detects a problem, the status LED located above the power button on the front of the computer
will ash in the following ways*:
1 Flash: No RAM is installed or detected. Or, the quick memory test failed. An LED will light up •
on the DIMM riser card next to the aected DIMM or empty DIMM slot.
3 Flashes: A RAM bank failed extended memory testing. An LED will light up on the memory •
riser card next to the aected DIMM.
Troubleshooting: Try reseating the memory DIMMs. Check memory installation instructions for
proper installation order. Swap aected DIMM with known good DIMM.
*Note: The status LED lights up when the power button is depressed at startup. Do not count this
light as one of the diagnostic ashes. The memory riser card diagnostic LEDs will also ash briey
when the computer is started up or shut down and when it goes in and out of sleep mode. This
is normal behavior.