LED 1 indicates that trickle voltage from the

LED 1 indicates that trickle voltage from the power supply has been detected. This LED will be ON when the computer is turned off and your power supply is working correctly.
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 LCD display are communicating. This LED will be ON when the computer is turned on and video signal is being generated.


LED 4 lights only if the computer detects an over-temperature condition. This LED will be OFF when the computer is turned on and running at the correct temperature.

могу сервиц мануал дать, схем там нет, траблшутинг чартс, симптомс, фру номера, *взорванные* виды итп.
archive.macfixitforums.com/ubbthreads.php/topics/473048/2
support.apple.com/kb/HT2173 (не ISIGHT но направление истинное)