Apple power mac g5 june 2004 User Manual

							
Power Mac G5 Troubleshooting 177

Power-On Self Test: RAM and Processor Verification
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 flash in the following ways*:
1 Flash: No RAM is installed or detected.
2 Flashes: Incompatible RAM types are installed.
3 Flashes: No RAM banks passed memory testing. 
4 Flashes: No good boot images are detected in the boot ROM (and/or there is a bad  
sys config block).
5 Flashes: The processor is not usable.
* Note: The status LED lights up when the power button is depressed at startup. Do not count 
this light as one of the diagnostic flashes.
Front Panel Board Troubleshooting
Certain no power symptoms can sometimes be caused by a failed front panel board or power 
button. However, troubleshooting these parts by swapping them out with known-good 
parts can be time-consuming. An alternative approach is to build a simple front panel board 
troubleshooting tool, as illustrated, and then use the procedures described below to test the 
board and button before actually replacing them.
The tool consists of a known-good front panel board, with a known-good power button and 
front panel board cable attached. 
To use the tool in troubleshooting the front panel board and power button, do the following:
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178 Power Mac G5 Troubleshooting

Shut down the computer.
Disconnect the installed front panel board cable from the logic board.
Connect the front panel board cable from the troubleshooting tool to the logic board.
Try to start up the computer by pressing the power button on the troubleshooting tool.
Then proceed with the front panel board troubleshooting steps as described in the “Symptom 
Charts” in this chapter.
Power Supply Verification
To power on, the computer’s logic board requires a “trickle” power of +5V. If the system fails to 
power on, first reset the PMU. Then follow the procedure outlined below to determine whether 
the problem is related to the power supply.
Note: To verify the power supply, you need a volt meter. 
Remove the power cord from the computer.
Open the computer, lay it on its side with the access side facing up.
Remove the front inlet fan assembly.
Remove the black plastic cap covering the 24-pin power supply cable connector (the P1 or 
largest connector). The cap fits tightly over the connector. To remove it, rock the cap gently 
forward and backward as you lift up. 
Note: This is a top view of the connector when it is plugged into the logic board.
Press the release latch on the connector and disconnect the cable from the logic board.
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Power Mac G5 Troubleshooting 179

Plug a known good power cord into the computer. Do not turn on the computer.
On the power supply cable connector: connect the black lead of the volt meter to pin 23 and 
connect the red lead of the volt meter to pin 1.
Note: This is a bottom view of the connector when it is unplugged and facing up.
The volt meter should measure approximately +5V. If you do not get a reading of +5V, recheck 
the volt meter connections and measure the voltage again. If the voltage is still not present, 
replace the power supply.
Pinouts
Power Supply P1 Connector
Pin #SignalPin#Signal
1+5Vstb13GND
2GND14Power ON
3FANtach15GND
4GND16EMPTY
5EMPTY17GND
6GND18RTNaud 
(GND)
7+12Vaud (12V2)19GND
8GND20+5V sense
9+3.3V sense21GND
10GND22-12V
11GND23GND
12EMPTY24EMPTY
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180 Power Mac G5 Troubleshooting

Power Supply P2 Connector
Pin#SignalColorPin#SignalColor
1+3.3VOrange9+5VRed
2+3.3VOrange10+5VRed
3+3.3VOrange11+5VRed
4+3.3VOrange12+12V3Yellow
5Reserve13+12V3Yellow
6+12VfanYellow14+12V1Yellow
7+12Vfan(12V2)Yellow15+12V1Yellow
8+25VWhite16RTNfan(GND)Black
Power Supply P3 Connector
Pin#SignalColorPin#SignalColor
1+5VRed5+5VRed
2GNDBlack6GNDBlack
3GNDBlack7GNDBlack
412V2Yellow8+12V2Yellow
Front Inlet Fan Connector
Pin#Signal
1FAN CPU Cpu AF MOTOR
2FAN CPU AF TACH
3FAN GND
4FAN 12V
5FAN CPU BF MOTOR
6FAN CPU BF TACK
7TEMP SENSE D-
8TEMP SENSE D+ 
						

							
Power Mac G5 Troubleshooting 181

Front Panel Board Connector
Pin#SignalType
125V 
2V-GND 
3FW TPATwisted Pair Shield 110 
Ohm
4FW TPA +Twisted Pair Shield 110 
Ohm
5CHASSIS GND FW
6CHASSIS GND USB 
7FW TPBTwisted Pair Shield 
100 Ohm
8FW TPB+Twisted Pair Shield 
100 Ohm
9USB PWR 
10USB GND 
11USB Twisted Pair Shield 60 
Ohm
12USB+Twisted Pair Shield 60 
Ohm
13LED 
14PWR BTN 
15AUDIO SENSE 
16AUDIO COMTwisted TRI
17AUDIO RIGHTTwisted TRI
18AUDIO LEFTTwisted TRI 
						

							
182 Power Mac G5 Troubleshooting
Optical and Serial ATA Hard Drive Cable Connectors 
PowerOpticalSP1 
(HD1)
SP2 
(HD2)
Pin#ColorPin#ColorPin#ColorPin#Color
1BLK4BLK
2BLK3BLK
3BLK1BLK
4BLK2BLK2BLK
5BLK3BLK3BLK
6BLK1BLK1BLK
7BLK4BLK4BLK
Media Bay Temperature Sensor Cable
7 Pin ConnectorSignal 5 Pin Connector4 Pin Connector
13.3V11
2[ ]G B CLK2
3] [G B DAT2
4GND42
5OVER TEMP5
6DOOR AJAR 13
73.3V SLEEP4 
						

							
Power Mac G5 Troubleshooting  183

Symptom Charts
How to Use the Symptom Charts
The Symptom Charts included in this chapter will help you diagnose specific symptoms related 
to the product. Because cures are listed on the charts in the order of most likely solution, try 
the cures in the order presented. Verify whether or not the product continues to exhibit the 
symptom. If the symptom persists, try the next cure. 
Note:  If a cure instructs you to replace a module, reinstall the original module before you 
proceed to the next cure.
Important:  The only way to shut off power completely to the computer and display is to 
disconnect their power plugs from the power source. Make sure the power cords to the 
computer and display are within easy reach. 
Startup Failures
When testing a computer for the following symptoms, remove the side access panel so you can 
better observe or listen for fan movement.
Note: Be sure to check the “DDR Memory” and “Power-On Self Test” topics in the General 
Information section of this chapter. Incorrect installation of DIMMs or incompatible memory will 
not allow the system to start up correctly. For information on how to correctly install DIMMs, see 
the “Memory (DIMMs)” topic in the Take Apart chapter.
Important: For troubleshooting purposes, Power Mac G5 (June 2004 Dual 1.8 GHz) computers 
and earlier models may be started up and diagnosed with a single processor installed in the 
upper processor slot. All other models covered by this manual must be started up with both 
processors installed.
Single Power Mac G5 Processor InstalledBoth Power Mac G5 Processors Installed
Original Uni 1.6 GHzJune 2004 Dual 2.0 GHz
Original Uni 1.8 GHzJune 2004 Dual 2.5 GHz
Original Dual 1.8 GHzEarly 2005 Dual 2.0 GHz
Original Dual 2.0 GHzEarly 2005 Dual 2.3 GHz
June 2004 Dual 1.8 GHzEarly 2005 Dual 2.7 GHz 
						

							
184  Power Mac G5 Troubleshooting

Note: The following symptoms and cures apply to Power Mac G5 computers in this manual 
except the Power Mac G5 (June 2004 Dual 2.5 GHz/Early 2005 2.7 GHz) computers. For startup 
failures for these models, see “Startup Failures for Power Mac G5 (Dual 2.5 GHz/Early 2005 2.7 
GHz)” later in this section.
Power-on LED does not illuminate when power button is pressed, fans do not 
spin, and there is no boot tone or video
Verify power outlet is good.
Replace power cord.
Reset the logic board. Refer to “Resetting the PMU on the Logic Board” in this chapter.
Verify power supply cables are fully connected.
Check for trickle voltage on the power supply connector. Refer to “Power Supply 
Verification” in this chapter. If verification fails, replace power supply.
Reseat front panel board cable.
Verify that processors are properly seated.
Verify that processors’ mounting screws are properly tightened. 
Replace front panel board cable.
Test the front panel board and power button using the front panel board troubleshooting 
tool. Refer to “Front Panel Board Troubleshooting” in this chapter. If the computer starts up 
correctly, go to step 11. Otherwise, go to step 14.
Test whether the front panel board or power button is at fault. Remove the installed front 
panel board and swap it for the known-good front panel board in the front panel board 
troubleshooting tool. Then connect the troubleshooting tool to the logic board of a 
known-good Power Mac G5 and start it up using the tool. If the computer does not start up 
correctly, go to step 12. Otherwise, go to step 13.
Replace front panel board.
Replace power button.
Replace logic board.
Replace power supply.
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Power Mac G5 Troubleshooting  185

Power Mac G5 (June 2004): Power-on LED illuminates when pressed in, but goes 
out when button is released, fans spin, and there is no boot tone or vid\
eo
Verify that the processors are properly seated.
Verify that the processors’ mounting screws are properly tightened. 
Remove the processors and check for damage to the logic board under the processors. If you 
see damage (see example below), replace the logic board. 
 
Note: For the Power Mac G5 (June 2004 Dual 2.0 GHz), go to step 5. For single-processor 
computers, go to step 6.
Remove lower processor. If the computer starts up correctly, go to step 5. Otherwise, go to 
step 6.
Replace lower processor.
Replace upper processor.
Check for trickle voltage on the power supply connector. Refer to “Power Supply 
Verification” in this chapter. If verification fails, replace power supply.
Replace logic board.
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186  Power Mac G5 Troubleshooting

Power-on LED illuminates when power button is pressed but fans do not spin (\
or 
spin only momentarily) and there is no boot tone or video
Reseat video card. (Make sure video card is fully inserted in connector and end of card is 
secured by the connector latch.)
Reset logic board. Refer to “Resetting the PMU on the Logic Board” in this chapter.
Verify power supply cables are fully connected. 
Note: For the Power Mac G5 (June 2004 Dual 2.0 GHz) and Power Mac G5 (Early 2005), go to 
step 5.
Remove lower processor (if installed). If the computer starts up correctly, go to step 5. 
Otherwise, go to step 7.
Reseat lower processor.
Replace lower processor.
Reseat upper processor.
Replace upper processor.
Check for trickle voltage on the power supply connector. Refer to “Power Supply 
Verification” in this chapter. If verification fails, replace power supply.
Replace logic board.
Power-on LED illuminates when power button is pressed and fans spin 
continuously but there is no boot tone or video
Reseat video card. (Make sure video card is fully inserted in connector and end of card is 
secured by the connector latch.)
Verify speaker cable is fully seated.
Reset logic board. Refer to “Resetting the PMU on the Logic Board” in this chapter. 
Note: For the Power Mac G5 (June 2004 Dual 2.0 GHz) and Power Mac G5 (Early 2005), go to 
step 5.
Remove lower processor (if installed). If the computer starts up correctly, go to step 5. 
Otherwise, go to step 7.
Reseat lower processor
Replace lower processor
Reseat upper processor
Replace upper processor.
Replace logic board
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