Arduino destroyed and all stepper drivers destroyed

Hi,

I wonder if anyone can think of any reason why my Arduino (Mega 2560) and all stepper motors on a RAMPS 1.4 all have been destroyed.

I was moving an end stop, and had switched all motors to off in Pronterface, but suddenly the 12V (20A) PSU fan came on, indicating power was being taken.
The stepper drivers started to get hot even though the motors were not moving at all.
I turned the 12V PSU off at the mains, and the turned it back on again, and the fan came on again on the PSU and then there was smoke from the Arduino.

I had a spare Arduino, so I plugged it in, but have found that all the stepper drivers have been destroyed. Well 1 of them works only in one direction, all the others don't work at all.

I've had to order a replacement RAMPS 1.4 and all stepper drivers, but I'm concerned in case this happens again, as its expensive to fix :-(


Is it possible for the Arduino to send commands to the stepper drivers which don't cause the motor to move, but causes them to draw large currents and hence be destroyed ??

Thanks.