Picar-S Rear Wheel direction did not change

Dear All
while assembly i did the rear-wheel-test. while it works fine for the wheel connected to
Channel A of the Motor Driver Board it fails on Channel B. Thus, wheel is speeding up and slowing down twice but keeps the direction over the whole circle.
Measurings say that the voltag behave at input pins MA and MB vs GRND is exactly the same. So wireing to that point seems to be correct.
anything else to check or did i pick up a set with a defect motor driver?

Do you mean that the A motor can work normally, but the B motor of the B interface does not work?
You can try swapping the motor and the interface. If the A motor is replaced with the B interface, and the B motor is replaced with the A interface, and the A motor cannot work, but the B motor works, it is an interface problem.
If A motor is switched to B interface, B motor is switched to A interface, B motor cannot work, and A motor works, it is a motor problem.

thats exactly what i did. Motors seem to work fine but as soon as i attach them to interface B its not working correct anymore.
I guess there is not much i can do except a waranty claiim?

Maybe the B interface of the motor driver module is damaged, arrange customer service to contact you, and send you a replacement motor driver module.