I have a 2013 Mac Pro [build date Jan 2014] with ProFire D300s, 32GB Ram, 512Gb SSD. I purchase secondhand 9 months ago for cheap as the base line 4 core standard config nMP. I’ve since pulled it apart twice and upgraded the CPU to a Hex 1650 v2 and most recently a Xeon 2667 v2. It’s a great reliable little Trash Can but with one annoying quirk that every so often it will just restart! This is totally random, but usually when the display has gone to sleep as I play relaxation music @ night to help me sleep. It’s done it with all 3 CPUs so I guess I can rule that Mod out of the equation. I have a 27” Cinema Display connected to the USB & thunderbolt port , Old school USB Apple Keyboard and Mouse and a AkiTiO thunder2 quad mini enclosure. I’ve tried various combinations of eliminating all but the basic peripherals but the issue still happens. Reset SMC, nvram, Techtool Pro, memtest, Clean installs, Different OS/OS X versions etc etc It always passes the online diagnostic without issue. I’ve also run the ASD 3S159 tests [both OS X and EFI versions] whenever I’ve swapped out the CPUs without any apparent fault. The restarts occur maybe once every week or two and only ever happened twice while I was actually using the machine. It seems unassociated with heavy loads as I’ve given it a thrashing with Heaven, Geekbench stress test and CPU Test for prolonged periods without a hiccup! The Mac is powered on 24/7. It just purrs away happily until it decides to restart >:< It’s not a freeze or panic but more as if one has purposefully selected to restart from the menu. [Like a soft reboot]. Can't seem to find anything sinister in the logs. Anyone else have a nMP with a similar code or habit? I know the Apple diagnostic minus figure codes are meant to represent a Hardware fault but I just can’t seem to reproduce this behaviour.