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When I plug my malfunctioning iMac in and press power, the Mac chime sounds, display turns on with white background, and the spinning noise of the hard drive whizzes; however, the display turns black and the computer turns off immediately afterwards. The closest related topic I could find is on iMac Intel 21.5" EMC 2308 will not turn on. Should I go ahead and attempt a PRAM battery replacement, or might there be a different approach to solving my issue?
You’ll need to checkout the onboard Diagnostic LED’s so see whats happening. Your PRAM battery could be bad if you’ve left the system unplugged from power or use a switched surge/power strip for long periods. If you’ve not unplugged it and you only have a power stip Vs a surge suppressor your power supply may have gotten hit. But I think we are jumping ahead here ‘:-} Lets check out the LED’s, follow this guide iMac Intel 21.5" EMC 2308 Logic Board Replacement Follow it to Step 10. Locate the right SO-DIMM holder, just to the right of it you’ll find a strip of black tape which is covering the LED’s.
Here’s a breakdown of the onboard diagnostic LED’s: LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. 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 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. Lets know what you find.
