オリジナル投稿者： Sean Wren ,
Paul I,ll save you the trouble. See Diagram below. The are four diagnostic LED’s located on the logic board. The LED meanings are as follows, but if LED #1 and LED #2 are on then the power supply is OK. You can only see the LED’s through the vent holes to the left of the memory modules on the bottom of the iMac. I had to make the room completely dark to be sure if they were on or not. All of mine were off and I tested that there was power coming out of the cable and into the imac with a multi meter [image|1694706] LED Functions LED #1 • Indicates that the trickle voltage from the power supply has been detected by the main 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 the computer has been shut down or put to sleep. The LED will turn off only if the AC power source 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 and that logic board voltage regulators are functioning properly. 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 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 display, then the LCD panel, the LED backlight board, or the cables between might be installed incorrectly or need replacement.