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I have a 2015 iMac 27” that just stopped turning on, the fans don’t spin the hard drive dosent make a noise, nothing, I changed out the power supply and still nothing, I also don’t see the 4 LEDs people are talking about being lit. We tried this with cables and outlets we know work too.
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Ouch! Did you test the AC output from the line feed to the power supply?
You should see the onboard diagnostic LED’s #1 lit if its not then your system is just not getting power. Here’s the guide on the LED’s:
LED 1 = Power is available.
If no LED is visible:
Disconnect the power cord from the computer and wait 15 seconds to reset the power supply and LED status. Reconnect the power cord and check the LED status again.
Verify the AC source.
Verify that a known-good power cord is connected.
Verify the cable connection between the AC inlet and the power supply. Verify the cable connection between the power supply and the logic board. Verify the power supply.
LED 1 + LED 2 = Power is available and the system is turned on. If the second LED is not visible when the power button is pressed:
Verify that the power button is connected to the power supply.
Verify power button functionality.
Verify the cable connection between the power supply and the logic board. Verify the power supply.
Verify the logic board.
LED 1 + LED 2 + LED 3 = Power is available, the system is turned on, and the GPU was found.
If the third LED is not visible after the system is turned on:
Verify whether the boot chime is present and fans are running when turned on (reset the SMC and PRAM and verify backup battery voltage for proper startup).
If the POST boot chime is not heard, go to the No Startup symptom flow. If the POST boot chime is heard, go to the No Video symptom flow.
LED 1 + LED 2 + LED 3 + LED 4 = Power is available, the system is turned on, the logic board is communicating with the GPU, and the internal LCD was found.
If the fourth LED is not visible after the system is turned on:
Verify the internal DisplayPort cable (eDP) connections between the LCD panel and the logic board. Inspect the LCD display cables for cable damage.
Verify external video functionality and proceed according to the result:
If an external display works, verify/replace the LCD panel.
If an external display does not work, verify/replace the logic board.
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I will give it a look today thank you Dan
So I checked the LEDs and we don’t have any lit up, I tried it in multiple outlets that we know work as well as with different cords
Then the socket in the back of the case and/or the leads to the power supply are bad. Time to pull out the DVM and measure the voltages Very carefully!! at the power supply AC plug.
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