Apple iMac G5, 20-inch - Manual (Page 261)

iMac G5, 20-inch Troubleshooting - 37 Symptom Charts
10. 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
step 11 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.
11. 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.
Continue to step 12.
No: Continue to step 11 to reset system power management.
12. 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. Continue to step 14.
No: Go to the next step.