Apple Self Repair Guides

Accessing the Diagnostic LEDs

• RepairSurge Auto Repair Software

The iMac G5 (20-inch iSight) has four built-in diagnostic LEDs on the main logic board that can help you troubleshoot the computer. Follow the steps below to access the LEDs.

1. Shut down the computer and disconnect all cables except the power cord.
2. Place a soft, clean towel or cloth on the desk or flat surface. Grasp the sides of the unit and slowly lay it screen-down on the cloth, with the bottom facing you.
3. Raise the stand and use a Phillips #2 screwdriver to loosen the two captive screws that secure the memory access door. Remove the access door.
4. Turn over the unit and place it screen-up, with the bottom facing toward you.
5. Tilt up the front bezel and use a T8 torx screwdriver to remove the three bezel mounting screws.

6. Stand up the unit. Using the plastic access card, unhook the bezel locking mechanism in one upper corner of the front bezel, and pull the bezel slightly away from the rear housing. Note: You must Insert the access card through the vent in the rear housing as shown below, and push it up and back until the latch releases.

7. Repeat step 6 to release the locking mechanism in the opposite upper corner.

8. Lay the unit screen-up on an ESD mat, with the bottom facing toward you. Lift up the top of the bezel and pull it slightly toward you to separate it from the top of the rear housing.

Lift the front bezel straight up to remove it. Then swing the bezel upright onto its top edge so you can disconnect two cables that tether the bezel to the rest of the unit. Caution: Make sure the memory eject rings are not protruding from the bezel when you lift it or you could bend or damage the rings. Also, do not use excessive force when removing the front bezel or you could break the locking mechanisms. If you feel resistance when lifting the bezel, repeat step 3 until each locking mechanism audibly unlocks.

10. Disconnect the two camera board connectors.

1. To protect the computer from electrostatic discharge, ground yourself by touching the metal frame around the display panel. Caution: Always discharge static electricity before you touch any parts or install any components inside the computer.
2. Carefully peel the lower EMI shield off the bottom edge of the rear housing. Use a black stick to help peel back the shield.

13. Remove the speakers. The LEDs are under the right speaker.

1. The four labelled diagnostic LEDs shown below.
2. The four labelled diagnostic LEDs shown below.

• LED 1: Indicates that trickle voltage from the AC power inlet to 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 main logic board has established communication with the LCD display.
• LED 4: Indicates a processor over-temperature condition. The system will shut down when this LED turns on.

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