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Model A1311 / Mid 2011 / 2.5 & 2.7 GHz Core i5 or 2.8 GHz Core i7 Processor

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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.

Thanks

Answer this question I have this problem too

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Did you perchance change the hard drive and not install the required thermal sensor (this will cause run away fan issues).

What system are you running and did this happen after you attempted a system upgrade?

Will it boot from an external USB source running a maximum of Sierra?

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Hi Mayer,

Here is the brief story. I originally added an SSD add in drive behind the Optical drive and noticed some issues. I removed the SSD and the cables, closed up everything and ran the AHT and got an error for the CPU fan. Replaced the CPU fan, no luck didn’t spin up., checked everything again with the display off to see if the CPU was spinning. The computer started and the optical drive fan went nuts but the cpu fan didn’t, I shut it down and re-assembled. After I put everything back together I pressed the power button and that is when my heart sunk… it will only start up and get halfway through the boot progress bar and then it shuts down…. :( Did anything happen by starting it with the display panel not attached? I also checked the LEDs and they seem to be working properly… Not sure what is next to do.

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What system are you running and did this happen after you attempted a system upgrade?

Will it boot from an external USB source running a maximum of Sierra?

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Thanks Mayer. I have El Capitan on it. I also tried to boot from 2 external hard drives with no luck. It does the same thing, starts with the Apple logo and then halfway through it just shuts down. I opened it again today and rechecked every cable and reassembled again with no luck. Not sure if a logic board would fixit. Not sure what else to do to troubleshoot. All 4 leds light up OK during startup.

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Boot from an external USB drive with a clean system on it and see if the problem persists

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