Apple MD094LL/A manual LED Functions, LED #1, LED #2, LED #3, LED #4

LED Functions

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 remain OFF only if the AC power source is missing or disconnected , if the logic board is disconnected from the power supply, or if the power supply board 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 should be 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.

2010-09-09 iMac (27-inch, Mid 2010) — General Troubleshooting 30