Just to share my mistake smoking smiley
For my dual extruder I use NEMA 11 stepper motors, 0.67 Amp/phase.
These light stepper motors can easy go down when powered with a higher current as specified. Per mistake I fired one up with 1.5 amp and immediately one phase was gone.
When it happens you can conclude this by measuring the resistance from the 2 phases. (see motor spec) Both phases should be close to equal. Mine should be 6 ohm and measured 2.3 and 6 ohm.
Good luck printing