Apple | Power Mac G5 (Late 2005) | User manual | Power Supply Verification

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To power on, the computer’s logic board requires “trickle” power. If the system fails to power on,
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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.
•
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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.
•
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LED 3 should be on and red, indicating that the main power is OK and within regulation.
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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.
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with or get caught in the blades of the fans.
1.
Remove the power cord from the computer.
2.
Open the computer, and lay it on its side with the access side facing up.
3.
Remove the metal G5 heatsink cover (let the unit cool before attempting measurements).
4.
Plug a known good power cord into the computer and press the power button on the front
of the unit.
5.
Measure the voltages as indicated in the following tables.
Power Mac G5 (Late 2005) Troubleshooting — General Information 134
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
Voltage
Positive Lead
Ground Lead
3.3 V
Tab 1
Tab 4
5.1 V
Tab 2
Tab 4
0V
Tab 3
Tab 4
0V
Tab 4
Tab 5
0V
Tab 5
Tab 4
0V
Tab 6
Tab 4
0V
Tab 7
Tab 4
12 VDC
Tab 8
Tab 4
12 VDC
Tab 9
Tab 4
Nominal
Min
Max
+3.3 VDC
3.14 VDC
3.48 VDC
+5.1 VDC
4.85 VDC
5.35 VDC
+12 VDC
11.4 VDC
12.60 VDC
+12 VDC
11.4 VDC
12.60 VDC
Power Mac G5 (Late 2005) Troubleshooting — General Information 135
CPU Terminals CPU A
Voltage
Positive Lead
Ground Lead
12 V
Terminal 1
Terminal 2
0V
Terminal 2
Tab 4
Nominal
Min
Max
+12 VDC
10.8 VDC
13.2 VDC
Voltage
Positive Lead
Ground Lead
12 V
Terminal 1
Terminal 2
0V
Terminal 2
Tab 4
Nominal
Min
Max
+12 VDC
10.8 VDC
13.2 VDC
CPU Terminals CPU B
Power Mac G5 (Late 2005) Troubleshooting — General Information 136