User Guide

iMac (27-inch, Late 2009) — General Troubleshooting 26
2009-12-16
LED Startup Sequence
LED #1 = Power available.
If no LED is visible:
Verify AC source •
Verify known-good AC cable is connected•
Verify cable connection between AC inlet and power supply•
Verify cable connection between power supply and logic board•
Verify power supply•
LED #1 + LED #2 = Power available, and system is powered on.
If second LED is not visible when power button is pressed:
Verify power button connection to logic board•
Verify power button functionality•
Verify cable connection between power supply and logic board•
Verify power supply•
Verify logic board•
LED #1 + LED #2 + LED #3 = Power available, system is powered on, and video card found.
If third LED is not visible after power on:
Verify that the MXM video card is seated properly•
Verify logic board•
LED #1 + LED #2 + LED #3 + LED #4 = Power available, system is powered on, video card
found, and internal LCD found.
If fourth LED is not visible after power on:
Verify cable connections between LCD panel and logic board•
Inspect LCD display cables for cable damage •
Verify external video functionality, and according to result check the following items:•
-If external display works then verify/replace the LED backlight board
-If external display works then verify/replace the LCD panel
-If external display does not work verify/replace the logic board