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1.83 GHz Core Duo or 1.83, 2, or 2.16 GHz Core 2 Duo A1208 (EMC 2104/2110/2114/2124)

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Diagnostic LED 2 dimly lit before power button pressed, will not boot

iMac 17” 2 GHz A1208 does not boot, no chime, no fans or other mechanical activity. Opened it up to see the diagnostic LEDs. Upon plugging in, LED 1 lights up normally, and LED 2 lights up at about half brightness and before I touch the power button. I have not been able to find any documentation on the two observed behaviors in LED 2 (on only DIMLY, and on BEFORE I touch the power button). What does this mean? Bad PSU? Bad logic board? I have one of each on order. Only “repair” I’ve done on it so far is swap out the clock battery. Thanks in advance for your help.

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@tony_

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

No Power

The iMac (17-inch Late 2006) will not turn on. The display remains black and there are no sounds from the fans or drives.

1. Verify the power outlet is good. Plug a different device into the socket to ensure there is power, or plug the iMac into another outlet. Does the iMac power on now?

Yes: Resolved. Bad outlet.

No: Go on to the next step.

2. Check the power cord. Use a known good power cord. Does the iMac power on now?

Yes: Your power cord has failed. Replace the AC power cord.

No: Go on to the next step.

3. Check the connection of the power cord on both ends. Verify that the power cord is securely plugged into both the AC outlet and back of the computer. Does the iMac power on now?

Yes: You may have a loose fit to your power cord. Replace the AC power cord and test.

No: Go on to the next step.

4. Follow instructions in the General Information chapter to reset the SMC. Does the iMac power on now?

Yes: Issue resolved.

No: Go on to the next step.

5. Remove and reinstall the SO-DIMM memory modules, located in the bottom of the computer. Does the iMac power on now?

Yes: Issue resolved.

No: Go on to the next step.

6. Remove the RAM access door, front bezel, and lower EMI shield to gain access to the three diagnostic LEDs. See “Diagnostic LEDs” in the General Information chapter for complete instructions on this procedure.

7. Plug the power cord into the iMac and the power cord into the AC outlet. Check to see if LED #1 is On or Off.

LED #1 is On: This indicates that the power supply is getting good power from the AC outlet.

Go on to the next step.

LED #1 is Off: This indicates that either the power inlet assembly or the power supply should be replaced.

8. Press the power button. Check to see if LED # 2 comes On, comes on momentarily, or stays Off.

LED # 2 is On: The Power Supply is functioning. Go on to the next step.

LED # 2 comes on momentarily or stays Off: Replace the Power Supply.

9. At this point in the Power On process, you should hear a boot chime and see the front LED on the computer light up. When the main logic board and LCD panel communicate to deliver video, the front LED should go off, and LED # 3 should be on. Does the Front LED go off?

Yes: The LCD and main logic board have communicated. If there is no picture on the display, follow “No Video” troubleshooting.

No: Your logic board is not communicating with LCD panel. Go on to the next step.

10. Check to see if LED # 3 is On or Off.

LED # 3 is On: The logic board is communicating with LCD panel. Follow “No Video” troubleshooting.

LED # 3 is Off: The logic board is not communicating with LCD panel. Reseat the LVDS cable and test again. If the issue persists, replace the main logic board.

Right now from what you are describing it does sound like a bad power supply, but it’s Apple so there will always be surprises. Let us know what you find out after your diagnostics.

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Comentários:

Hi oldturkey03, thanks for your reply. I have seen the instructions you’ve copied above, but unfortunately they don’t describe what it means for LED 2 to turn on when the computer is first plugged in before the power button is touched. The above information makes it seem like that should never happen. I suppose LED 2 coming on dimly could be read the same as it coming on “momentarily,” indicating a bad power supply. Hopefully a different PSU will clear it up, but the behavior is still strange.

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