User Guide

Mac Pro Troubleshooting — General Information 147
Diagnostic LEDs
The Mac Pro logic board includes a set of LEDs to help service providers troubleshoot the
computer. The LEDs are located toward the rear of the logic board, under the memory cage, next
to PCI card slot 1. You can view these LEDs by removing the computer’s side access panel and
looking through the memory cage to the logic board below. LEDs 2, 3, 4, and 5 are normally o
and will automatically illuminate if an error occurs. To read LEDs 1, 6, 7, and 8, you must press the
DIAG_LED button, which is adjacent to the LEDs. To press the DIAG_LED button, use the nylon
probe tool (Apple part number 922-5065).