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Original post by: Ray ,


Shutdown during iMac boot


I’m having an issue with my 2011 iMac 21.5 2.7ghz. I replaced the CPU fan that was not working for some time and after replacing when turning on the iMac, it displays the apple logo and the progress bar goes to about the center of the bar and then the system just abruptly shuts down. I checked all connections and also checked the 4 LEDs on the mother board while referencing the Repair Manual and all seems OK, no lights out.

I also tried all modes, safe, recovery, AHT but no luck same thing, shuts down during startup . I did try verbose mode and the last thing  displayed is “Previous shutdown cause: -1”

Not sure what next…how can I tell if the GPU is OK? Also is there a way to tell if it is a thermal sensor?

Any troubleshooting tips would be appreciated.



iMac Intel 21.5" EMC 2428