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HI guys My iMacs Screen isn’t coming on. LED 1 and 2 come on and so does LED 3 however after about 30 secs it goes off and LED 4 never comes on. Any Advice on what to do or check? Thanks
To double check things see if you get an image using an external display. But from your symptoms it sounds like the GPU board has failed. From Apples support docs: LED #3 - Indicates that computer and video card are communicating. This LED will be ON when computer is communicating properly with video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the backup battery (on front of logic board) may need to be reseated, or the video card might be installed incorrectly or needs replacement.LED #4 - Indicates that computer and LCD panel are communicating. This LED will be ON when computer is turned on and video signal is being generated. If LED #4 is ON and there is no image on display, then LCD panel, LED backlight board, or cables between LCD and logic board or backlight board might be installed incorrectly, or need replacement. Here is the IFIXIT guide you’ll need to follow: iMac Intel 21.5" EMC 2389 GPU Card Replacement And here are your choices for replacement boards: ATI Radeon HD 4670 (256MB) - Apple P/N 661-5539ATI Radeon HD 5670 (512MB) - Apple P/N 661-5546
