@greezy91 it could still be a power supply issue. LED 2 will only turn on when it gets the power from the power supply. So start with that before you replace the logic board.
• Indicates that the trickle voltage from power supply has been detected by 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 computer has been correctly shutdown, the 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 power cord is kept connected and AC power source is present.
Disconnecting the power cord and plugging it back will turn back this LED ON , even if
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 from the AC receptacle, or if the power supply board is faulty.
• Indicates that computer is turned on. This LED will be ON as long as computer is turned on
(but is not asleep) and power supply and voltage regulators are working correctly.
• Indicates that computer and video card are communicating. This LED will be ON when
computer is communicating properly with video card. If LEDs 1 and 2 are ON and you heard
the startup sound, but LED 3 is OFF, then the backup battery (on back of logic board) may
need to be reseated, or the video card might be installed incorrectly or needs replacement.
• Indicates that computer and LCD panel are communicating. This LED will be ON when
computer is turned on and video signal is being generated. If LED#4 is ON and there is no
image on display, then the LCD panel, the LED backlight board, or the cables between LCD
and logic board or backlight board might be installed incorrectly, or need replacement.