Chosen Solution
First sorry for my not so perfect English. I have a iMac which fell down to the ground, it looks very bad, the display is complete broken. But, the iMac is still working with an external monitor. I removed the broken display, but if I start the system without the display it starts very slowly (the known kernel _start Problem). I think it’s a something I missed. Does anyone know how to fix the problem in OS-X ?
The display has a few thermal sensors which are no longer working as you’ve taken the display off. This is what is expected! As the SMC thinks the system has a failure and is now running in safe mode. To fix this you will need to replace the display LCD Late 2015 iMac 21.5" non-Retina, Apple P/N 661-02989 and you’ll need [linked product missing or disabled: IF173-005-1] and here’s the IFIXIT guide: iMac Intel 21.5" EMC 2889 Display Replacement
