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  1. #1


    Member Since
    Dec 18, 2009
    Posts
    3
    Does anyone know what the status LED's are on the logic board of an iMac, Mine is not starting, the superdrive cycles but then nothing, when I push the power button 3 of the 4 led's light up like the logic board is working, but nothing happens. I found this About the iMac G5 diagnostic LEDs but its not for my mac, its for an earlier model.

    Update* when I put the installation cd in the superdrive it spins up and revvs out like its trying to read it, but still no lcd or logic board, do the trouble shooting lights work on the logic board even it its fried. Is there some component that would make my system all wonky like this?

  2. #2

    powermac G5's Avatar
    Member Since
    Oct 17, 2008
    Location
    Bowmanstown, PA
    Posts
    256
    Specs:
    *27" imac C2D 3.0/1TB/16GB**Mac Pro Octo 2.8/4x1TB/16GB**Mac Pro Quad 2.66/2x1TB/8GB**iPhone 4*
    LED #1
    • Indicates that the trickle voltage from the power supply has been detected by the main logic board. This LED will remain ON whenever the iMac is connected to a working AC power source. 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 source 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. 5. LED #4 should be On when the video card and LCD display have communicated properly to produce a video image. Is LED #4 On or Off?
    LED # 4 is On: The video card and LCD display have communicated to LCD video. In this case, there is a problem with the backlights in the panel or the inverter. Verify the four inverter cables are fully inserted into the cable connectors to the inverter and check that the wires have not been pinched. Replace the inverter first and then the LCD panel if the problem persists.
    LED # 4 is Off: The video card and logic board are unable to communicate to generate video. Replace the video card. If the issue persists, replace the LCD display.
    5. LED #4 should be On when the video card and LCD display have communicated properly to produce a video image. Is LED #4 On or Off?
    LED # 4 is On: The video card and LCD display have communicated to LCD video. In this case, there is a problem with the backlights in the panel or the inverter. Verify the four inverter cables are fully inserted into the cable connectors to the inverter and check that the wires have not been pinched. Replace the inverter first and then the LCD panel if the problem persists.
    LED # 4 is Off: The video card and logic board are unable to communicate to generate video. Replace the video card. If the issue persists, replace the LCD display.
    6. Unplug the iMac and remove the SDRAM. Replace with known good SDRAM. Plug the iMac back in and power the unit on. Does the front LED go off after a few moments now?
    Yes: Replace the original SDRAM and test again. If the front LED does not go off with the only the original SDRAM installed, replace the SDRAM. If the LED is now reliably going off after a
    few moments, but yet you still do not have any video, go to step 7.
    No: If the LED remained on, the main logic board is not communicating with the LCD panel to generate video. Replace the main logic board.
    7. If video is displayed normally on an external display but not on the iMac internal display panel, replace the LCD display.

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