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I've had my 2011 Mac Mini for a while. About a year ago the internal HDD decided to give up. Oh well.

I just now finally got around to being able to replace the hard drive. I decided to go with an SSD (a Samsung 850 PRO, got it from Amazon here). Installed OS X 10.10.4 (have an application that is broken on 10.10.5+ unfortunately).

So after all of this I've been using it for about a day. Over that day it has seemingly restarted itself several times while it was idle and nobody was looking (meaning the monitor was off and nothing was connected over VNC, but apps, mainly chrome, were running - nothing uncommon and that I haven't used on other Macs with no issues).

The only clue I can see (not that I exactly know what I'm looking for) is in Console. I get an error message stating kernel[0]: Previous shutdown cause: -128.

I did have previous errors with this machine where it would randomly restart every once and a while, where I couldn't figure out a rhyme or reason, but these were way more infrequent and happened no more often or differently than other Macs I have. Certainly not 3 or 4 times in a day.

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Shutdown cause -128 is "hardware" related; most times, I have noticed it's related to memory.

What you can try:

  • NVRAM and SMC Reset. Hold CommandOptionPR for about 20 seconds while turning on from a powered off state. The boot chime should sound about 3 times; then release and boot normally. To reset the SMC, shut down, unplug your Mac mini for 30 seconds, then plug back in and restart.
  • Reseat the memory modules (you may have inadvertently caused a bad connection when replacing the drive)
  • Run Apple Hardware Test (AHT). Hold the D key while booting from a powered off state with the AC adapter connected. Make sure you run the extended tests.

If your memory tests come back with errors, remove one module and try again. Make sure you tests each module individually in each slot individually. You want to see if the problem (if it exists) stays in the same location (slot is bad) or moves (memory is bad)

  • Thanks, Allan. I'll give that a shot. Just curious, is there a list of error codes somewhere? I found one but it looks like it was from the 80s. – lightbord Jun 19 '17 at 0:41
  • Officially the -128 error code is a general error code, and literally means userCanceledErr. In theory, a userCanceledErr is reserved only for instances where the user has explicitly cancelled an action via the esc key or cmd-period keyboard shortcut. However, in practice, it often doesn't work this way and can be triggered by a range of hardware 'actions' (as Allan indicates in his answer). For example, in much earlier versions of macOS, trackpad users were known to trigger this because dragging their finger along the trackpad wasn't received properly by the receiver. – Monomeeth Jun 19 '17 at 11:26
  • So, assuming you didn't cancel anything, I'd be curious as to what external hardware you're using? If running AHT doesn't identify a problem, try using a process of elimination to narrow down the possible cause. I would still follow Allan's advice re testing your memory. If no joy, try a different keyboard, mouse, etc. While it's tempting to just assume it's the SSD, the reality is that you haven't used the Mac mini for a long time and your Mac mini did randomly restart every once and a while even beforehand, so it's quite possibly something you've been using for a long time. – Monomeeth Jun 19 '17 at 11:27

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