How can I distinguish SOD from ShutDown?

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http://forum.xda-developers.com – Hi All, I have a rooted/custom ROMmed N7. For some reason, most of the Custom Roms that I'm using just makes my N7 SOD. It usually happens if I have in activity for more than 2 hours but I also had some right after a few minutes. I've used different ROMs with different kernel and it was all the same. So it usually happens more than 5 times a day. Now it came to me that my N7 could be defective since I can't tell if it was shutting down or SOD. I never had heat issues with so I don't think it is shutting down because of heat. Is there a log somewhere that I could find that would (HowTos)