My IMAC a1076 needed the smc reset because the power button was unresponsive. I managed to get the power button to start the fans but thats about all it does. The orange status light in the front bezel on the bottom right is orange and the screen stayed black to whole time.
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Take the back off using this guide:
iMac G5 20" Model A1076 Rear Panel Replacement
Examine the 24 cans (capacitors for swelling and/or leakage. There are two CUDA buttons one for restart and one for reset on the logic board, Try both.
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