Chosen Solution
This is on a late 2009 iMac 27" A1312. Was replacing the ODD. When I put it back together there is no display at all. It chimes and boots, I got into it via Screen Sharing with my laptop. I am currently backing it up. Checked all cables and temp sensors, they appear fine though the Vsync cable is looking a little worn. My main question, since the display is completely dark, no faint image, no lED bars, nothing at all on screen, does it sound like a power supply problem, or if the connector on the logic board right over the video card is boo booed, and not letting any video signal in to the monitor will it prevent startup of the lcd itself. I don’t know the order of steps for power up of the LCD. Also does the front plastic have any sensors on it that might prevent the kid from powering up? Thanks, George Harrison III
Depending on the iMac model, it has either three or four built-in diagnostic LEDs on the main logic board that can help you to troubleshoot the computer. The LEDs are located either to the right of the battery or to the right of the RAM and may be covered with black tape. 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. Note: this LED is not used on systems with the integrated graphics 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. _ I noticed you already checked it with an external display and found a picture. Please tell us what LEDs are lit. I think I left you a good enough explanation of what they indicate.
To help isolate the problem hook it up to an external monitor. Check the diagnostic lights to the right of the RAM and let us know your results.
