Sorry to open this thread up again. I have a very similar issue that may be closely related.
My Mac Mini 2011 with Intel i7 and 6630m randomly reboots during startup and normal use. Sometimes I can run Blender on it heavily before it fails, but it always does after some amount of time.
I have replaced the PSU as well as the HD cable along with putting an Intel SSD inside.
I hear some people talking about cold solder joints on some chip, is that the Intel BD82HM65 Platform Controller Hub?
If I were to pursue the logic board repair would this be the first thing to try?
Thanks in advance for everyone's willingness to help!