Chosen Solution
Hey guys, I have an iMac emc 2428 that is not powering up. The unit was left in sleep mode overnight and the next day it wouldn’t power up. When the power button is pressed nothing happens, no noises or fan spin. I’ve tried multiple known working power cords and different AC outlets. I’ve reset SMC and tried leaving it unplugged overnight and tried the next day, still no signs of power. Apparently there are diagnostic LEDs that I am trying to locate. I removed the RAM and looked through the bottom vents and RAM slots but couldn’t see any LEDs. My guess is the power supply is dead, therefor no LED. Or the issue is I’m not looking in right spot. I have purchased suction cups but haven’t opened the iMac until I know it’s necessary. Any help would be greatly appreciated! Thanks, Adam
This series is a bit different than the older models, the diagnostic LED’s are located about mid point in the logic board and looking at the system standing are also backwards! The most right LED is #1.
Diagnostic LED’s marked in green and the order from this perspective is: 4-3-2-1 (zoom the image) Basically, it’s setup so if you rest the system on its back and lift the display up using a foam wedge to hold the display you should be able to see the LED’s Follow this IFIXIT guide iMac Intel 21.5" EMC 2428 Display Replacement follow the guide to Step 4 and then carefully lift the display up a bit. Are you able to see any lit LED when you power up the system? If not your power supply is gone. Update (03/30/2017) LED #1 Indicates that the trickle voltage from power supply has been detected by main logic board. This LED will turn ON when you connect the iMac to a working AC power source. The LED will remain ON as long as the computer is ON or asleep. LED #2 Indicates that computer is turned on. This LED will be ON as long as computer is turned on (but is not asleep) and power supply and voltage regulators are working correctly. 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. LED #1 = Power available If first LED is not lit: Disconnect the power cord from computer, then reconnect it to reset the LED status.Verify AC power source.Verify known-good power cord is connected.Verify cable connection between AC inlet and power supply.Verify cable connection between power supply and logic board.Verify power supply. LED #1 + #2 = Power available, and computer is powered on. If second LED is not lit when power button is pressed: Verify power button cable connection to logic board.Verify power button functionality.Verify cable connection between power supply and logic board.Verify power supply.Verify logic board. In your case you’ve proved the issue is not the power button and the system is getting power, so the issue is more likely the logic board. Update (03/30/2017) @gamefreak701 - Here’s the power supplies header marked in green:
And here is the pins voltages you’ll need to see:
Sounds like it could also be the Power buttons continuity. Maybe the power button is bad and its shutting itself back off when the button is pressed?
