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Recently my iMac won’t power on at all. I opened it and noticed that none of the diagnostic lights are powering up. Not even the 1st led. I tested the psu with a multimeter on the psu pins. pin readings are shown below: Pin 1 - Ground Pin 2 through 4 - No voltage Pin 5- 12.04v Pin 6- No voltage Pin 7 - 3.315v Pin 8 through 9 - No voltage Pin 10 - 3.315v Pin 11 through 15 - 12.04v Pin 16 - No voltage I also checked the power cord and small cable that connects to PSU and it has power going through them fine. I would like to know if my iMac power supply is dead, needs to be replaced or is it another issue? Any help would be greatly appreciated.
With your power supply re-connected lets check the onboard diagnostic LED’s to see what they tell us. They are well hidden in this series as they are taped over!
Here’s a breakdown of the onboard diagnostic LED’s: LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty.LED 2 - Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.LED 3 - Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement. What are they telling you??
