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Contribution d'origine par : oldturkey03 ,

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Samantha, start with this:"

Reset your computer’s PRAM (Parameter RAM):

If y -- our iMac is on, turn it off by holding the power button until the unit powers off. You should hear the fans go quiet.

-- While the computer is off, with your left hand, hold down the Apple key, the Option key next to it, and the letter “R” key on the keyboard. When you have these keys all pressed down, push the power button with your right hand and then quickly move that hand to hold down the letter “P” on the keyboard. Keep these four keys pressed while the computer starts up.

-- Make sure you hold down the four keys (P - R - Apple - Option) while the computer is starting up. When you hear the computer’s start up chime for the second time, you can let go of the keys on the keyboard.

-- If you didn’t hear at least two startup chimes, go to the top of this section and begin again. It’s important that you hear two startup chimes when performing this procedure.

This indicates that you have successfully reset the computer’s PRAM (Parameter RAM).

Reset the SMC (Formerly SMU).

-- Turn off the computer by choosing Shut Down from the Apple menu, or by holding the power button until the computer turns off.

-- Unplug all cables from the computer, including the power cord.

-- Wait 15 seconds.

-- Plug in the power cord while simultaneously pressing and holding the power button on the back of the computer.

-- Let go of the power button.

-- Press the power button once more to start up your iMac.

Diagnostic LEDs

The iMac (20-inch Late 2006) has three built-in diagnostic LEDs and a front power-on/sleep LED on the main logic board that can help you to troubleshoot the computer.

To Access the Diagnostic LEDs:

1. Follow the take apart instructions to remove the RAM access door, front bezel, and lower EMI shield.

2. Locate the SO-DIMM slot and LVDS video connector. The three diagnostic LEDs 1, 2, and 3 are located below the battery and to the right of the memory slot. Note that the LEDs are marked 1, 2, 3 as show below. An additional front bezel LED is located in an opening at the center of the right speaker.

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 LCD display are communicating. This LED will be ON when the computer is turned on and video signal is being generated.

Front LED • Indicates that the computer has power but no video signal (e.g., the computer is starting up or the display has entered Sleep mode, turning off the video signal). This LED will pulse when the entire system has entered Energy Saver mode.

Let us know what you find. The buzzing could be coming from your power supply or your inverter. Try an external monitor and see if that shows you anything.

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