Model A1224 / Mid 2007 and Early 2008 / 2, 2.4, or 2.66 GHz Core 2 Duo processor

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black screen, can hear it power up

imac 20" mid-2007 aluminum EMC2133 - black screen. LED1 ON before (plugged) and after start, no chime sound, LED 2 and LED 3 ON right after start, goes OFF momentarily, fan stops, all come ON again shortly after. LED 4 OFF all the time. Can hear HD, Optical DR after start. Intermittently when started screen comes up for 1 sec and then goes black. 1 out of 20 times. Replaced the logic board. No change. Replaced HD. No change. is this a power supply issue? thanks.

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Ercan, here are the diagnostics code. Should be a comment and not an answer, but its to long:-)

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 video card are communicating. This LED will be ON • when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.

LED #4

Indicates that the computer and the LCD display panel are communicating. This LED will be • ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.

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