Apple power mac g5 late 2005 User Manual

							
Power Mac G5 (Late 2005) Troubleshooting — General Information 141
Power Supply Verification
To power on, the computer’s logic board requires “trickle” power. If the system fails to power on, 
first reset the SMU (remove power cord for approximately two minutes). If the unit still doesn’t 
power on, follow the procedure outlined below to determine whether the issue is related to the 
power supply. 
Verify trickle power
Diagnostic LED 4 indicates the presence of trickle power required by the logic board to begin the 
startup process.  
Remove the clear plastic air deflector (fans will go to high while door is removed).
LED 4 should be on and yellow, indicating that trickle voltage is present.
Verify Power Supply is providing power
Diagnostic LED 3 indicates that the main power is OK and within regulation.
Plug in AC power cord, and press the power-on button on the front panel.
Remove the clear plastic air deflector (fans will go to high while door is removed).
LED 3 should be on and red, indicating that the main power is OK and within regulation.
Voltage Measurements
Note: Due to the size and location of the Power Mac G5 (Late 2005 Quad) processor module, 
it isn’t possible to get access to the power bus bar screws to check the voltages. The following 
procedure can be used only for Power Mac G5 (Late 2005 Dual 2.0/2.3 GHz) computers.
If the computer has trickle power and is capable of starting up, you may measure the voltages 
available from the power supply. Use a volt meter to take measurements at the screws that 
attach the power bus bar to the logic board, and at the terminal connections that provide power 
to the processor module. 
Warning: During this procedure, do not let any fingers or the voltage probes come in contact 
with or get caught in the blades of the fans.
Remove the power cord from the computer. 
Open the computer, and lay it on its side with the access side facing up. 
Remove the metal G5 heatsink cover (let the unit cool before attempting measurements). 
Plug a known good power cord into the computer and press the power button on the front 
of the unit.
Measure the voltages as indicated in the following tables. 
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Power Mac G5 (Late 2005) Troubleshooting — General Information 142
Location of Bus Bar Tabs and Terminals
Note: This is a top view of the main logic board with the processor module removed. You must 
test the voltages with the processor module installed. 
MLB Power Bus Bar
VoltagePositive LeadGround Lead
3.3 VTab 1Tab 4
5.1 VTab 2Tab 4
0 VTab 3Tab 4
0 VTab 4Tab 5
0 VTab 5Tab 4
0 VTab 6Tab 4
0 VTab 7Tab 4
12 VDCTab 8Tab 4
12 VDCTab 9Tab 4
NominalMinMax 
+3.3 VDC3.14 VDC3.48 VDC 
+5.1 VDC4.85 VDC5.35 VDC 
+12 VDC11.4 VDC12.60 VDC 
+12 VDC11.4 VDC12.60 VDC
  
						

							
Power Mac G5 (Late 2005) Troubleshooting — General Information 143
CPU Terminals CPU A
VoltagePositive LeadGround Lead
12 VTerminal 1Terminal 2 
0 VTerminal 2Tab 4
NominalMinMax 
+12 VDC10.8 VDC13.2 VDC
 
CPU Terminals CPU B
VoltagePositive LeadGround Lead
12 VTerminal 1Terminal 2 
0 VTerminal 2Tab 4
NominalMinMax 
+12 VDC10.8 VDC13.2 VDC  
						

							
Power Mac G5 (Late 2005) Troubleshooting — Symptom Charts 144
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.
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.
Check that diagnostic LED 4 is on when the power cord is connected and the air deflector is 
removed. 
Replace power cord.
Check that diagnostic LED 3 is on when the power cord is connected and the air deflector is 
removed.
Reset the logic board. Refer to “Resetting the Logic Board” in this chapter.
Verify power supply cables are fully connected and power bus bar screws are tightened.
Verify that processors are properly seated. Check diagnostic LED 1 and/or LED 6.
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Power Mac G5 (Late 2005) Troubleshooting — Symptom Charts 145
Verify that processors’ mounting screws are properly tightened.
Reseat front panel board.
Test whether the front panel board or power button is at fault. Remove the installed front 
panel board and swap it for a known-good front panel board.
Replace front panel board.
Replace power button.
Replace power supply.
Replace logic board.
Power-on LED illuminates when pressed in, but goes out when button is released, 
there is no boot tone or video, but you can hear a small click
Remove the power cord.
Open the computer and lay it on its side.
Remove the processor heatsink cover.
Using an ohm meter, measure the resistance across Terminal 1 and Terminal 2 for CPU A. 
(Refer to the Power Supply Verification photo for terminal locations.) Hold the meter’s 
probes on the terminals for 5 seconds minimum. Nominal resistance readings should be 
above 200 ohms. If the resistance is below 10 ohms, replace the power supply.
Check for trickle voltage from the power supply. Refer to “Power Supply Verification” in this 
chapter. If verification fails, replace power supply.
Verify that the processor module is properly seated. Check diagnostic LED 1 and/or LED 6.
Verify that the processor mounting screws are properly tightened. 
Replace the power supply.
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.) For video cards that require power cables, check that they 
are connected.
Reset logic board. Refer to “Resetting the Logic Board” in this chapter.
Verify power supply cables are fully connected and power bus bar screws are tightened.
Check diagnostic LED 1 and LED 6 for processor connection.
Reseat processor and check for bent pins.
Check for trickle voltage from the power supply. Refer to “Power Supply Verification” in this 
chapter. If verification fails, replace power supply.
Replace logic board.
Replace processor.
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Power Mac G5 (Late 2005) Troubleshooting — Symptom Charts 14
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.) For video cards that require power cables, check that they 
are connected.
Verify speaker cable is fully seated.
Reset logic board. Refer to “Resetting the Logic Board” in this chapter.
Check diagnostic LED 1 and LED 6 for processor connection
Replace processor
Replace logic board
Power-on LED illuminates when power button is pressed, fans spin, and boot tone 
chimes, but there is no video
Reseat video card. (Make sure video card is fully inserted in connector and end of card is 
secured by the connector latch.) For NVIDIA Quadro FX 4500 graphics card, check that power 
cord for card is connected.
Reset PRAM (restart computer while holding down Command-Option-P-R keys until second 
boot tone chimes)
Reset logic board. Refer to “Resetting the Logic Board” in this chapter.
Replace video card
Replace logic board
Power-on LED does not illuminate when power button is pressed, but fans spin, 
boot tone chimes, and there is video
Reseat front panel board
Replace front panel board
Replace logic board
Replace power supply
Power-on LED illuminates, fans spin up, no boot tone, and the system shuts down 
within a few minutes
Check diagnostic LED 1 and LED 6. 
Reseat the processor and check for bent pins
Replace the processor
Replace the logic board
Replace the power supply
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Power Mac G5 (Late 2005) Troubleshooting — Symptom Charts 14
Power-on LED illuminates, fans and processor pump run harder, there is no boot 
and the system shuts down within a few minutes
Remove the processor and look for loss of fluid on the absorbent liner on top of the power 
supply. If you see drops of fluid, replace the processor, otherwise go on to the next step.
Reseat the processor. 
Replace the processor
Replace the logic board
Replace the power supply
Fluid leak is suspected and the computer is plugged in
Unplug the computer
Put on rubber gloves if handling a liquid cooling module that is leaking or suspected to be 
leaking
Remove the processor
Wipe the spill using rags, paper towels, or other suitable material. Contain and dispose of the 
cleaning materials according to locals laws and regulations.
Wash the skin with running water
Replace the processor
Replace modules that show corrosion to the traces or solder joints.
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Power Mac G5 (Late 2005) Troubleshooting — Symptom Charts 14
Fans  
Individual fan failure
Replace fan 
Exception: The media blower located between the optical and hard drives cannot be 
replaced. You must replace the enclosure for this part.
Replace logic board
All fans run at high speed
Check for proper ventilation around the exterior of the computer.
Check that the clear plastic air deflector is in place.
Run Apple Service Diagnostic (refer to “Thermal Calibration” earlier in this chapter).
Processor fans run at high speed
Verify that the clear plastic air deflector door is in place.
Verify that the white sensor label is not damaged and is in place on the lower right tab of 
the air deflector door. If necessary, replace the air deflector.
Verify that the air deflector sensor board is operating properly. 
Note: You can differentiate a bad sensor label from a bad sensor board by the following: 
Remove the air deflector door. Slide a folded piece of paper through the slot in the enclosure 
where the right tab of the air deflector would normally be inserted. If the red LED goes out 
(but stays on with the door in place), the sensor label on the door is missing or damaged. 
Check the sensor cable connection on the logic board (second from right connector located 
directly below the hard drives).
Replace the logic board.
Replace the air deflector sensor board.
Computer goes to sleep for no apparent reason
Two additional symptoms: The system log typically includes a message similar to: “PowerMac7,3 
Thermal Manager: Thermal Runaway Detected: System Will Sleep.” The customer may also note 
that the fans ramp up to a higher speed shortly before the computer sleeps. 
Check that the fans are operating. 
If the system log still reports Thermal Runaway, run Apple Service Diagnostic (refer to 
“Thermal Calibration” earlier in this chapter).
Replace the processor module.
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Power Mac G5 (Late 2005) Troubleshooting — Symptom Charts 14
Other Failures
Air deflector sensor 
Reseat air deflector sensor board cable
Replace air deflector sensor board
Replace logic board
Optical drive 
Replace optical drive cable
Replace optical drive
Replace logic board
FireWire port (front panel A) 
Reseat front panel board
Replace front panel board
Replace logic board
Firewire port (rear AB) 
Replace logic board
Firewire port (rear BB) 
Replace logic board
Internal speaker 
Check speaker cable connection
Replace speaker/fan assembly
Replace logic board
USB 2.0 (front port) 
Reseat front panel board
Replace front panel board
Replace logic board
USB 2.0 (rear ports)
Replace logic board
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Power Mac G5 (Late 2005) Troubleshooting — Symptom Charts 150
Combo Card 
Reseat antenna cables connected to Combo card
Replace Combo card
Replace antenna card
Replace logic board
Audio IO (front headphones)
Reseat front panel board
Replace front panel board
Replace logic board
Audio IO (rear audio line in; rear audio line out) 
Check Sound settings in System Preferences
Replace logic board
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