LED #1
• Indicates that trickle voltage from power supply has been detected by logic board. This LED
will remain ON whenever the iMac is connected to a working AC power source. The LED will remain on even when computer has been shut down or put to sleep. The LED will turn off only if AC power source is disconnected or power supply is faulty.
LED #2
• Indicates that logic board has detected power from power supply when computer is turned on. This LED will be ON when computer is turned on and power supply and voltage regulators are working correctly.
LED #1 = Power available.
If no LED is visible:
• Verify AC source
• Verify known-good AC cable is connected
• Verify cable connection between AC inlet and power supply
• Verify cable connection between power supply and logic board
• Verify power supply
LED #1 + LED #2 = Power available, and system is powered on.
'''If second LED is not visible when power button is pressed:
• Verify power button connection to logic board
• Verify power button functionality
• Verify cable connection between power supply and logic board
• Verify power supply
• Verify logic board'''
Couple of checks you can do:" Disconnect AC cable then remove power supply and
carefully inspect connectors between AC inlet and power supply, then DC connectors and cables between power supply and logic board, for damage or poor connections.
Inspect power button and verify if it is properly connected to the logic board
Disconnect power button from logic board. Inspect cable and connector for damage. Verify continuity between the two pins of power button when it is pressed.
Press power button and Verify if system turns ON. You may alternately check for presence of a 12V DC signal between pin 11 and pin 1 of logic board when power button is pressed. If not, Replace DC power cable." Remember, I am not a Mac person, just a person who enjoys hardware from any manufacturer. Hope this helps, good luck. Hope this helps, good luck.