Arduino Uno + Arduino Motorshield Rev3 Shield-Power-Supply disconnected driving the motor what happends?

Other Hardware General Electronics
1

Hi a friend of mine is using an Arduino Uno with the Arduino motorshield Rev3 stacked on top of the uno to drive a stepper-motor. I tried to help him over a remote session.

The Arduino Uno got damaged for a not really known reason.

The 12V power-supply for powering the motorshield was switched OFF.
Is there a possability that the Arduino Uno got damaged because the motorshield was drawing too much current through the 5V-pin of the arduino?

I thought the onboard voltage-regulator of the Arduino-Uno has a overtemperature protection which would simply shut off the voltage regulator until cooled down then switching the voltage regulator back on.

2

As a wild guess, I would not expect the motor driver board to try and use the Arduino 5V as the motor power supply because the 12V supply wasn't there.