iMac G5: Troubleshooting when there‘s no picture on the display

If your iMac G5 turns on (you hear the startup sound and can hear the hard drive and fan working), but there is no picture or video on the display, follow these steps to troubleshoot the issue.

This article has been archived and is no longer updated by Apple.
  1. Press the space bar to make sure the computer isn't in sleep mode.
  2. Did the computer wake from sleep?
    • Yes: Put the computer to sleep again by choosing Sleep from the Apple menu, then wake the computer again to test. Check the Sleep settings in Energy Saver preferences to see when the computer is set to sleep.
    • No: Continue to the next step.
  3. Reset your computer's PRAM (parameter RAM) by doing the following:
    1. If you iMac is on, turn it off by pressing the power button until the computer turns off. You should hear the fans stop working.
    2. Press the power button to restart your computer and immediately hold down the Command, Option, P, and R keys simultaneously. Make sure to keep holding down all four keys while the computer starts up.
    3. When you hear the startup sound for the second time, let go of the keys. If you don't hear a second startup sound, repeat these three steps again; the second startup sound indicates that you have successfully reset the computer's PRAM.
  4. Does the computer display video after you've successfully reset the computer's PRAM?
    • Yes: Choose Restart from the Apple menu and make sure the computer is now working correctly.
    • No: Continue to the next step.
  5. Remove the computer's back cover to access the diagnostic LEDs (lights) on the main logic board. See Chapter 4 of your iMac G5 User Manual for instructions on how to remove the back cover.
  6. With the power cord and back cover removed, locate the diagnostic LEDs 1 through 4 above the large, white arrow on the main logic board.

  7. Plug the power cord into the iMac G5 and into a working electrical outlet. LED 1 should turn on if your computer is receiving power. If LED 1 is off, see iMac G5: Troubleshooting when your computer won't turn on for further troubleshooting information.
  8. Turn the computer on using the internal power button (press the small, metal button below the fan cover as shown below).

  9. When the computer starts up, LED 2 will turn on after you hear the startup sound. This means the logic board is processing power correctly. If LED 2 does not turn on, skip to step 11 for instructions on resetting the System Management Unit (SMU). If LED 2 still doesn't turn on after resetting the SMU, see iMac G5: Troubleshooting when your computer won't turn on for further troubleshooting information.
  10. LED 3 turns on last, indicating that the logic board and LCD assembly have communicated, and that the LCD is ready to receive video. Does LED 3 turn on?
    • Yes. This means that your miplane is working correctly to produce video. Skip to step 12.
    • No: Continue to step 11 to reset the SMU.
  11. Press the SMU reset button (the small, metal button next to the internal power button, shown below) to reset system and power management.
    Note: If you're using an iMac G5 (Ambient Light Sensor) computer, your SMU was already reset when you unplugged and replugged the computer. You won't see an SMU reset button to press, and that's ok, as it's already been done. (If you aren't sure what sort of iMac you have, click here for help.)

    After pressing the SMU button, does LED 3 turn on?
    • Yes: Press and hold the power button until the computer turns off. Restart the computer and confirm that LED 3 turns on again. Continue to step 12.
    • No: If LED 3 is off, this means that your logic board needs to be replaced. Please schedule a service appointment with either an Apple Retail Store or an Apple Authorized Service Provider.
  12. Press the internal power button until the computer turns off. Unplug the power cord from the computer and replace the back cover. Return the computer to the upright position. Plug in the power cord and turn on the computer. Do you see video on the display now?
    • Yes: Restart the computer and make sure that the computer is working properly.
    • No: Continue to the next step.
  13. Turn the display at an angle to you and look closely at the display. Is the display completely black or can you see a dim light or glow to the display?
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