Well there are a few troubleshooting steps you may of done already though you can follow these steps and get back to see where you are to your device i have several here in my school and do this every once in a while and when I perform these tasks those processes our Macs power back on, but lets see what happens.
1. Verify AC power source plug another device to wall outlet or plug
2. Disconnect all peripherals and press and hold power button for 15 seconds, this is performing an SMC Reset.
3. Verify user's power cord and have one available to replace if helps
4. Determine if computer is in power-on state by checking all of the following : (When i do this i press the power button a good second and then wait for a good 30 seconds and it turns on.
Caps Lock LED on wired keyboard
Fan spinning sound
hard drive spin (if hard drive present)
optical drive reset/disc detect seek
display backlight on or flash
external display activity, if available
Thunderbolt disk mode operation (on newer models)
if the steps above did not resolve the matter and unit is still off, try the following with only the basic connections usb keyboard and mice corded prefer and power cable.
Performed the SMC Reset unplug all devices and press and hold power button for 15 seconds and then leave unplugged for up to 1 hour recommended, but 30 minutes will do fine - just that apple recommends an hour and understand the power supply contains a high voltage capacitor that may remain charged so performing the SMC will assist in this process.
If this process fails please perform the same process with a different power cord and outlet, if unit still fails
Locate the Diagnostic LED's on logic board With AC power cord connected to computer, verify whether diagnostic LED #1 is on, indicating power supply is providing power to SMC and logic board.
- If there is no power LED after performing an SMC Reset, result is a power supply
- If there is power led, Verify that the DC power cable and HDD power cable are plugged into the correct ports on the logic board. These cables have identical connector ends and could accidentally be switched.
You can differentiate these cables by the length of the wires between the connector and sheathing. The HDD power cable has more length of exposed insulated wires between connector and sheathing than the DC power cable.
And Finally since the unit is open you can Remove coin battery and AC power to computer. Wait 90 seconds, then restore AC power and attempt to power on computer.
- Note: On some iMac models, the coin battery is located on the back side of the logic board.
If unit still does not power on you are now at replacing the power supply or logic board, if you want to go more detail tell me what works as there are 3 more steps.
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