User Guide
Mac Pro Troubleshooting — Symptom Charts 158
Remove the computer’s side access panel and observe the diagnostic LEDs, specically LED 4.
4 and LED 5 (the CPU A and B Overtemp LEDs). Refer to “Diagnostic LEDs” in this chapter
for more information on how to locate and interpret these LEDs. If either of these LEDs is
ashing, this may indicate an initial processor over temperature condition. If either of these
LEDs is solidly on, this may indicate a chronic processor over temperature condition. Initial
processor over-temperature can cause symptoms such as sluggish computer performance. A
chronic processor over-temperature condition can cause the computer to hang completely.
Verify proper processor heat sink installation. (Refer to “5. Processor Heatsinks” in the Take
Apart chapter for more information.)
Verify all thermal sensors and their cables are properly connected, especially the ambient 6.
temperature sensor board.
Verify all fans are operating properly and are unobstructed, especially the front intake fan.7.
Other Failures
Optical drive
Try dierent optical media.1.
If two drives are installed, check the Master/Slave or Cable Select jumpers on both optical 2.
drives (this will depend on drive vendor). Both drives should be set to ‘Cable Select’ mode for
proper operation.
If two drives are installed, test one optical drive at a time by disconnecting one of the drives 3.
to see if the other one works.
Replace optical drive cable 4.
Replace optical drive 5.
Replace logic board 6.
Front Panel FireWire port
Reseat front panel board cables1.
Replace front panel board cables2.
Reseat front panel board 3.
Replace front panel board 4.
Replace logic board 5.
Rear FireWire port
Replace logic board