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Introduction

The 24-inch 2007 and 2008 iMac's have four diagnostic LEDs on the logic board that can help troubleshoot the computer. A little disassembly is required to locate and observe the LED's. This guide is based on information sourced from the applicable Apple service manual.

**LED interpretation is also applicable to the iMac Intel 20" EMC 2133 and 2210**

  1. Loosen the single Phillips screw in the center of the access door.
    • Loosen the single Phillips screw in the center of the access door.

    • This screw is captive in the access door.

    • Remove the access door from your iMac.

    • The glass panel is fixed onto the front bezel with fourteen magnets around its perimeter.

    • Stick two suction cups to opposing corners of the glass panel.

    • To attach the suction cups we sell, first position the suction cup with the movable handle parallel to the face of the glass panel. While lightly holding the suction cup against the glass, raise the movable handle until it is parallel with the other handle.

    • If your suction cups refuse to stick, try cleaning both the glass panel and the suction cup with a mild solvent such as Windex.

  2. Gently pull the glass panel straight up off the iMac.
    • Gently pull the glass panel straight up off the iMac.

    • The glass panel has several positioning pins around its perimeter. To avoid shearing these pins off the glass panel, be sure to only pull straight up during removal.

    • Be meticulous about cleaning the LCD and the inside face of the glass panel before reinstallation, as any fingerprints or dust trapped inside will be annoyingly visible when the display is on.

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  4. Remove the following 12 screws securing the front bezel to the rear case:
    • Remove the following 12 screws securing the front bezel to the rear case:

    • Eight 13 mm T8 Torx screws

    • Alternatively, you might have six 13 mm and two 25 mm T8 Torx screws

    • Four 25 mm T8 Torx screws

    • Alternatively, you might have two 25 mm (outer) and two 35 mm (inner) T8 Torx screws

  5. The front bezel is still attached to the iMac by the microphone cable. Gently lift the front bezel from its top edge off the rear case. It helps to use your thumbs to push down very gently on the corners of the display.
    • The front bezel is still attached to the iMac by the microphone cable.

    • Gently lift the front bezel from its top edge off the rear case. It helps to use your thumbs to push down very gently on the corners of the display.

    • Once the top edge of the front bezel has cleared the rear case, rotate the front bezel toward the stand and lift it off the rear case.

    • When reinstalling the front bezel, start at the lower edge and make sure it is flush with the rear case before lowering the top edge onto the iMac.

  6. Disconnect the microphone cable connector, removing tape as necessary.
    • Disconnect the microphone cable connector, removing tape as necessary.

    • For the front bezel to sit properly, be sure to tuck the microphone cable and connector into the void next to the camera board.

  7. To observe the LED's you need to apply power to the iMac with the front bezel off.  Please ensure you don't touch any part of the iMac or the exposed circuit boards while you have power connected.
    • To observe the LED's you need to apply power to the iMac with the front bezel off. Please ensure you don't touch any part of the iMac or the exposed circuit boards while you have power connected.

    • Locate the Diagnostic LED's between the RAM slots and the SATA connector.

    • The LED's are numbered 1-4 from left to right. You may need to move the SATA cable to get a clear view of the LED's.

    • If you are using this guide for iMac Intel 20" EMC 2210 and 2133 the LED's are located above the SATA connector and not as visible.

    • LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty.

    • 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 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 display 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 LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.

Conclusion

To reassemble your device, follow these instructions in reverse order.

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Richdave

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Hello,

I have iMac 2008 24" When I turn on the computer no startup sound but DVD / Motherboard / CPU Fan is still on. also two green LED is static on, anyone help me....

Raza

Syed Irfan Raza Abidi - Réponse

Does anybody know where I can buy the thermopads for the 4 chips on the video card. The ones it already had were all melted and can't reuse them. I appreciate your time and help. Thank you.

Jesus Juarez - Réponse

Does anybody know where I can buy the thermal pads to put on the 4 chips on the video card? Any help is very appreciated. Thank you.

Jesus Juarez - Réponse

Imac would not boot up (LED #1 lit only) about 9 months ago so I replaced PSU at that time. iMac was working fine until recently when it would not boot up again. Only LED #1 lit so I replaced the PSU again thinking this would solve problem……it did not. Only #1 stays lit and SuperDrive starts to spin yet no fans or chime or screen.

Question: Any other checks before logic board needs to be looked at or replaced. Is it worth replacing logic board on 10 year old iMac? How long and any special tricks?

Thanks from Florida.

Andreas - Réponse

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