[Q] Random Cycle Reboot

Hi to everyone!

I have a Samsung I9300T (Australian version). A few months ago I flashed my phone through CM Installer from stock Rom (Vodafone's Android 4.1.2) to CM 11 M2. And there were no problems.
A month ago I flashed CM 11 M6. And after upgrading from M2 to M6 my phone started rebooting at random times. In these moments, the display goes black, then the logo "Samsung S3" is displayed for a few seconds, then reboot again and it lasts permanently. I flashed cm m2 back, but this problem not solved.

I've made full wipe, installed M7, installed GApps, made full wipe. And it's still reboots.
I've reinstalled CWM recovery through ROM manager. And it's still reboots.
I've made full wipe. installed another ROM (not CM), made full wipe. And it's still reboots.
I've flashed default stock and recovery from vodafone (4.3) through Odin, and it's still reboots.

Please, help me with this trouble.

Thank you.

boomboomer said:

If it is still the same on a fresh install of stock firmware then it is a hardware issue.

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When I flashed a stock ROM, I found some files from CM ROM in phone memory. How can I make full format of all data in phone? I think some parts of old ROM make bugs. And maybe kernel was modified, may it cause these problems?