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No Video, No Startup Chime, 3rd LED is Off

Hello everybody,

i've got an iMac 20 inch (Late 2006) with a booting problem. After pressing the power button i can hear noises from the fan, harddrive and so on, but there is no video signal the screen stays dark and there is not the usual start up chime!

I did a little research and opened the iMac to locate the 3 service leds. When i start up the iMac only LED 1 and 2 are glowing and the white big LED on the front panel stays on. The third LED on the right hand side of the memory slots stays off.

I tried to reset the SMC according to the service manual i found here: on page 158, but this didn't help at all. All i got was a high spinning fan and still no video signal. After removing the power cord again, waiting, pluged it in again, powering up the high fan spinning was gone again.

At the moment i got only a wirless Keyboard, so i can't reset the PRAM. Is that right?

I removed both RAM memory bars, but still no luck. No video, no start up chime, no third LED. Not even a beep for the missing memory. The RAM memory work flawless in a old MacBook. Trying the memory of the MacBook in the iMac didn't helped too.

So, my question is: is the Logic Board or the Screen? Anything else i should try?

Thanks in advance for your help, suggestions and support.

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Bu iyi bir soru mu?

Puan 3
4 Yorum

I am having this exact same issue right now. Was this ever resolved?


I too have the same problem. Any answers Apple?


I am having the same problem I even bough a use imac and switched everything that I could and still nothing please we need help


Have a similar problem with A1207, without LED panel led 3 no light but external monitor good and show "?" because HDD its new. When put LCD panel led 3 its light, but no chime and black screen.

Apreciate some coments!



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LED 1 indicates that trickle voltage from the power supply has been detected. This LED will be ON when the computer is turned off and your power supply is working correctly.

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.

LED 4 lights only if the computer detects an over-temperature condition. This LED will be OFF when the computer is turned on and running at the correct temperature.

Inspect the 24 capacitors for bulging and/or corrosion. There was also a GPU problem on this one. The solder joint failed as the machine heated up and this can sometimes be repaired with a solder reflow. Take a look and let us know what you find. The LED's indicate a bad GPU (video card). This machine also has integrated video. The first thing I would check is the RAM to see that they are a matched pair and seated properly:

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Puan 4

4 Yorum:

Thank you for your reply, but that is a different iMac. I'm on a Late 2006 iMac. It's an Intel Mac and the last one with the white plastic front bezel. I've got only three diagnostic LEDs on the logicboard and the big white LED on the front.

As i mentioned before i already checked the RAM. That's not causing the problem.


Please give us the last three figures of your serial number


The last three figures of my iMac serial number are XCR.


I have repeated all the steps User Harry has stated with a similar Imac Serial ending in VUW . The only addition is: If you hold the power button on it will start flashing. If I remove the RAM the main indicator light will flash when the power is on, indicating some sort of self test is still functioning.


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Are there LED lights for the Early 2006 model? Got to agree with the overheat in late 2006 "suzy bake Apples" flip over MB hold soldering iron on contacts opposite Radeon 1600 GPU for 45 sec. to one min.. do thermal paste artic silvr. install smc fan controll (Macupdate) back in bussiness-add drill holes through the plastic where the slot is-does not show-probably was considered in design and rejected as too practical.

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