Late 2013 iMac failing ASD CPU test and shutting off
We had a late 2013 iMac come in with booting issues. It would go halfway and shut off.
I figured a bad update screwed things up so I reinstalled OS-X. Same thing. Ran Apple Service Diagnostic and it shut down on CPU test.
It would pass whetstone and fail on dhystone and linpack. To me this was open and closed CPU failure. Replaced the CPU and all was OK for a few days. It passed 21 iterations of ASD. Customer gets it back and it doesnt turn on again this morning.
Given that the CPU tests were failing, I don’t know what more it could be.. Another odd thing it does is once it shuts down, it will not turn on unless you do a NVRAM reset.