Mac Mini "unexpectedly shutting down"

Welcome to the Apple discussions.

Kernal panics are normally associated with bad memory, however, there are other reasons that can cause them. A good read on causes and fixes can be found at http://www.thexlab.com/faqs/kernelpanics.html

My mac mini has also started shutting itself down at odd intervals. This machine is just 2 years old. It was in the shop for repair 3 months ago, presumably for a bad hard drive but it was determined the RAM was bad, so that was replaced and presumably checked out ok. This computer runs my home automation and entertainment system, so it runs 24/7. Nothing in particular seems to make it shut down. It will do this any time of the day. I had suspected it was heat related but it just shut down and the room & unit is a moderate temperature. What's really annoying is it doesn't auto-power back on after this shut down. Those options are selected in System Preference. My best guess is the power supply (power brick) is failing. Thoughts?

The problem with diagnosing this issue is that it's neither clear what was wrong with the system when it was repaired, nor what was done to resolve it at the time. While these events may have nothing to do with the present issue, they may be directly related.

As an example - you say that the system was not hot when it recently shut itself down, but had the repair involved removal of the logic board and the thermal pad wasn't replaced (as described as a requirement in the service notes) then it would render the system far more likely to apparently random shutdowns, because heat would build up more quickly and trigger protective mode with little apparent heating. That would also explain why the restart options don't seem to work.

Thus it might be a good idea to ask the repairers exactly what they did to the system when they had it, before contemplating a potential fault in the power unit.