The computer will turn on but the display has no picture or color The boot chime the fan and hard drive activity can be heard

  1. Check if the computer is sleeping. Press the space bar to wake the computer from sleep mode.
  2. Did the computer wake from sleep?

Yes: Put the computer to sleep from the Apple menu and wake the computer again to test the settings. Check Energy Saver setting to see when the computer has been designated to sleep.

No: Continue to the next step.

3. Reset your computer's PRAM (Parameter RAM).

  • If your iMac is on, turn it off by pressing the power button in until the computer powers off. You should hear the drives and fans go quiet.
  • Wait for a few seconds.
  • While the computer is off, with your left hand, hold down the Apple key, the option key next to it, and the letter R. When you have them all pressed push the power button with your right hand and then quickly move that hand to hold down the letter P. Keep the four keys pressed while the computer starts up.
  • Make sure you hold down the four keys (P-R-Command-Option) while the computer starts up. When you keep all the keys held down, you will hear the startup chime over and over again (about every ten seconds) until you let go. After you hear the second chime, you can let go of the keys.
  • If you didn't hear at least two startup chimes, go to step one on this page and try again. It's important that you two startup chimes when performing this procedure. This indicates that you have successfully reset the computer's PRAM (Parameter RAM).

4. Does the computer display video after successfully resetting the computer's PRAM?

Yes: Problem resolved. Restart the computer from the Apple menu and make sure the computer is starting up properly.

No: Continue to the next step.

  1. Remove the back cover to access the diagnostic LEDs on the main logic board.
  2. With the back cover removed, locate the diagnostic LEDs 1 through 4 above the large yellow arrow on the main logic board.
  3. With the back cover removed, locate the diagnostic LEDs 1 through 4 above the large yellow arrow on the main logic board.
Mac Leds The Main Logic Board
  1. Plug the power cord into the iMac G5 and into a known good AC outlet. LED #1 should come on if your computer has been starting up properly. If LED #1 is Off, see iMac G5: Troubleshooting: No Power for further troubleshooting information.
  2. Turn the computer on by using the internal power button. Press the small, metal button under the fan cover as shown
Powerbook Wont Power
  1. When the computer starts up, LED #2 will light after you hear the boot chime indicating the logic board is processing power correctly. If LED #2 does not light, reset the SMU (System Management Unit). Refer to "Resetting the SMU" mentioned earlier in this chapter. If LED #2 remains off after resetting the SMU, your logic board needs to be replaced. Order and install the logic board for your computer.
  2. LED # 3 will light last indicating that the logic board and LCD assembly have communicated and the LCD is ready to receive video. Does LED #3 come on?

Yes: This indicates that your logic board is working correctly to produce video. Continue to step 14.

No: Continue to step 11 to reset system power management.

11. Reset the SMU (System Management Unit). Refer to "Resetting the SMU" mentioned earlier in this chapter.

After resetting the SMU, does LED #3 light now?

Yes: Press and hold the power button until the computer powers off. Start the computer again and confirm that LED #3 is reliably lighting. Continue to step 14.

No: Go to the next step.

12. Unplug the iMac G5 and remove the SDRAM. Replace with known good SDRAM. Plug the iMac G5 back in and start the unit by pressing the two internal power pins. Does LED #3 light now?

Yes: Replace the original SDRAM and test again. If LED #3 does not light with the original SDRAM, replace the SDRAM.

How Check Internal Power For Imac

No: Continue to next step.

13. Unplug the iMac G5 and remove the optical drive. Plug the iMac G5 back in and start the unit up from the internal power button. Does LED #3 light now?

  • Yes: This indicates the optical drive has failed. Replace the optical drive.
  • No: Replace the logic board.

14. WIth LED #3 on, turn the machine off by holding the internal power button until the unit powers off. Unplug the computer and reinstall the back cover. Return the computer to the upright position. Plug in the computer again and power on the computer. Does the computer have video now?

  • Yes: Restart the computer and make sure that the computer is operating properly.
  • No: Continue to the next step

15. 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?

  • Completely black: Replace the inverter
  • Dim or light glow: Replace the LCD panel.
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