@h4r1y0n0
make sure you check the power button etc. as well. the how to is included in the deep dive.
Diagnostic LEDs (A)
LED 1
Indicates that the trickle voltage from the power supply has been detected by the main logic board. This LED will turn on when you connect the iMac to a working AC power source. The LED will remain on as long as the computer is on or asleep.
When the computer has been shut down correctly, LED 1 behavior may differ:
If a startup event is scheduled in System Preferences/Energy Saver, LED 1 will stay on after a correct shutdown.
If no startup event is scheduled in System Preferences/Energy Saver, LED 1 will turn off and will stay off as long as the power cord is kept connected and an AC power source is present. Disconnecting the power cord and plugging it back in will turn this LED back on, even if the computer is still off.
After disconnecting and reconnecting the AC power source, this LED could remain off:
If the AC power source is missing or disconnected.
If the logic board is disconnected from the power supply or the AC receptacle.
If the power supply board is faulty.
LED 2
Indicates that the computer is turned on. This LED will be on as long as the computer is turned on (but is not asleep) and the power supply and voltage regulators are working correctly.
If no LED is visible:
Disconnect the power cord from the computer and wait 15 seconds to reset the power supply and LED status.
Reconnect the power cord and check the LED status again.
Verify the AC source.
Verify that a known-good power cord is connected.
Verify the cable connection between the AC inlet and the power supply.
Verify the cable connection between the power supply and the logic board.
Verify the power supply.
LED 1 + LED 2 = Power is available and the system is turned on.
If the second LED is not visible when the power button is pressed:
Verify that the power button is connected to the power supply.
Verify power button functionality.
Verify the cable connection between the power supply and the logic board.
Verify the power supply.
Verify the logic board.
Check the power supply temp sensor area as well as try the reset test pads by shortening out across the solder pads with a screwdriver or similar (bottom right on the board)
Following the deep dive troublshooting. At step 12 you can make determination if it is a power supply issue or the logic board (my money is on the power supply)
Here is the location of the reset pads (C)
pleasedontfront