As you had your system unplugged for awhile I would start off replacing the PRAM battery. Until you have a reliable PRAM voltage your system won’t fully start up. I assume you are getting a boot chime and fan.
Plug the power cord into the iMac G5 and into a known good AC outlet. LED #1 should come on if your computer has been starting up properly.
When the computer starts up, LED #2 will light after you hear the boot chime indicating the logic board is processing power correctly. If LED #2 does not light, go to SMU reset section below for instructions on resetting the SMU. If LED #2 remains off after resetting the SMU, your logic board needs to be replaced. Order and install the logic board for your computer.
LED # 3 will light last indicating that the logic board and LCD assembly have communicated and the LCD is ready to receive video. Does LED #3 come on?
* '''Yes''': This indicates that your logic board is working correctly to produce video'''.'''
* '''No''': Continue to SMU section to reset system power management.
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To reset the SMU - Plug in the power cord while simultaneously pressing and holding the power button on the back of the computer.
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Press the SMU reset button to reset system and power management. This is the small metal button below the internal power button as shown.
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After pressing the SMU button, press the internal power button to start up the computer. Does LED #3 light now?
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After the SMU start up the computer. Does LED #3 light now?
'''Yes:''' Press and hold the power button until the computer powers off. Start the computer again and confirm that LED #3 is reliably lighting.
As you had your system unplugged for awhile I would start off replacing the PRAM battery. Until you have a reliable PRAM voltage your system won’t fully start up. I assume you are getting a boot chime and fan.
Plug the power cord into the iMac G5 and into a known good AC outlet. LED #1 should come on if your computer has been starting up properly.
When the computer starts up, LED #2 will light after you hear the boot chime indicating the logic board is processing power correctly. If LED #2 does not light, go to SMU reset section below for instructions on resetting the SMU. If LED #2 remains off after resetting the SMU, your logic board needs to be replaced. Order and install the logic board for your computer.
LED # 3 will light last indicating that the logic board and LCD assembly have communicated and the LCD is ready to receive video. Does LED #3 come on?
* '''Yes''': This indicates that your logic board is working correctly to produce video'''.'''
* '''No''': Continue to SMU section to reset system power management.
Press the SMU reset button to reset system and power management. This is the small metal button below the internal power button as shown.
After pressing the SMU button, press the internal power button to start up the computer. Does LED #3 light now?
'''Yes:''' Press and hold the power button until the computer powers off. Start the computer again and confirm that LED #3 is reliably lighting.