[Solved] MK3S keeps restarting when activating Heatbed (over 40C)  

MK3S keeps restarting when activating Heatbed (over 40C)

Foreword:
”I spend the last couple of Weeks trying to find out what the issue was with my MK3S
and posting this, so it hopefully helps others with the same issue”.
Also this is my first Post and i couldn’t find anything on this exact same issue, so if this is a double Post etc. let me know. 

the Issue:
Printer keeps shutting off and turning right back on when activating Heatbed over 40C (Video):

https://vimeo.com/user163821408/review/666970710/a9a09d1187

(it works when used under 40C and it works for a short time over when gradually setting the
temperature higher in steps of 1-2C). 

what i did:
Checked Cables and Wiring
Inspected Mainboard for damage and burns
Inspected solder joints on Heatbed
Checked Fuses (on PSU and MB)
Checked Voltage out (PSU and MB)
Checked Thermistor
Reflashed Firmware (393, 3100, 3101)
Factory reset 
and lastly i swapped out the Mainboard.

All that didn’t help (actually made it worse - but that’s another Issue altogether).

Spoiler: the Problem appears to be a Short caused by a tiny hole in the Heatbed (Pictures) that I and everyone else overlooked!

Solution (temporarily): i but a piece of Hottape over the Hole just to confirm and it fixed the Issue.

I hope that helps !