Fan Not Working - How do I troubleshoot?

I now don't get error message booting into Apple Hardware Test, but get blank screen instead, nothing happens. Any fix for that?

I installed High Sierra on SSD from flash drive installer, just to see if disc would remain HFS journaled. It changed to APFS as online info indicated. So then, I restored original system that was running on HFS drive from Time Machine backup.

When I tried to open Apple Hardware Test, I got error: "Cannot Load EFI/DRIVERS/TestSupportefi"

Why would EFI disappear when it was on the unitialized SSD? Did HFS TM restore delete EFI? I tried to clone from Carbon Copy Cloner bootable High Sierra backup, but don't have the right version to clone to APFS drive.

I had a heck of a time getting Mac to recognize drive in the first place. Crucial support page indicated trouble with High Sierra, so I booted from by external USB backup of old Sierra system instead of High Sierra. I may have missed the "this disc is not intialized" message the first time in Sierra boot (don't think it ever appeared in High Sierra boot), but fortunately, eventually later tried again, saw the initialize message, clicked the button, and chose HFS Journaled, so I could install High Sierra from Apple installer, which of course reformatted drive to APFS.

I can boot just fine into Apple Hardware Test on SATA drive in MacBook Pro 2011, running exact same High Sierra system created on HFS Journaled and backed up to Time Machine.

Tried Option D instead of just D. Got spinning globe (like on MacBook Pro) as if Mini was going to boot into AHT, but then EFI error appeared as before with D Boot. Forgot to mention, that I reinstalled High Sierra from Apple installer and EFI error disappeared from D boot but did not fix, left with blank screen. I thought OSX reinstall was supposed to fix missing EFI?

Apple introduced a bug in the firmware and the newer OS's that messes up diagnostics! You found it and so far there is no solution.