Chosen Solution
iMac lntel 27 was working one day and was not the next. No noises, no changes, no power outages. Plugged into UPS. Other accessories still work plugged in. Not a heavy use computer, just family usage. It will do nothing with power button. Cord swapped, held button forever, nothing. Many idea’s would be appreciated, TIA.
At this point you’ll need to take the display off to see what the on-board diagnostic LED’s are telling you. Here’s how to take the dimply off iMac Intel 27" EMC 2429 Display Replacement
The LED’s are on the logic board to the right of the RAM slots and between the RAM slot and the HDD sata connector 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. Let us know what you see.
