Arduino Motor Shield Rev3 Motor B one direction not working

Other Hardware Motors, Mechanics, Power and CNC
1

I want to drive to DC motors.

I have an Arduino UNO and an arduino motor shield rev3.

Arduino motor shield current measurment jumpers are cut off (I need the Analog Input for other sensors)
The power jumper is also cut off.

I use 4 AA batteries (6V) for the motors and a 9V battery to power the Arduino.

Motor A works fine for both directions
Motor B works only when I set the B DIR PIN (13) to HIGH. (one direction) but not in the other.

I made a setup using only Arduino UNO, Arduino Motorshield, the two motors and power supply.

//MOTOR A PINS  (LEFTMOTOR)
#define MOTOR_A_DIR_PIN 12
#define MOTOR_A_PWM_PIN 3
#define MOTOR_A_BRAKE_PIN 9
//#define MOTOR_A_CS_PIN A0
//MOTOR B PINS   (RIGHT MOTOR)
#define MOTOR_B_DIR_PIN 13
#define MOTOR_B_PWM_PIN 11
#define MOTOR_B_BRAKE_PIN 8
//#define MOTOR_B_CS_PIN A1
void setup() {
  pinMode(MOTOR_A_DIR_PIN, OUTPUT);
  pinMode(MOTOR_A_PWM_PIN, OUTPUT);
  pinMode(MOTOR_A_BRAKE_PIN, OUTPUT);

  pinMode(MOTOR_B_DIR_PIN, OUTPUT);
  pinMode(MOTOR_B_PWM_PIN, OUTPUT);
  pinMode(MOTOR_B_BRAKE_PIN, OUTPUT);


  // Release the breaks... Just to be sure
  digitalWrite(MOTOR_A_BRAKE_PIN,LOW);
  digitalWrite(MOTOR_B_BRAKE_PIN,LOW);
 //Set direction for both motors
  digitalWrite(MOTOR_A_DIR_PIN, LOW);
  digitalWrite(MOTOR_B_DIR_PIN, LOW);
 //Send speed to both motors
  analogWrite(MOTOR_A_PWM_PIN, 250);
  analogWrite(MOTOR_B_PWM_PIN, 250);
  //Wait for a while
  delay(1000);
  // Stop the motors
  analogWrite(MOTOR_A_PWM_PIN, 0);
  analogWrite(MOTOR_B_PWM_PIN, 0);
}

void loop() {
  // put your main code here, to run repeatedly:
}

Am I missing something on the code?

I am afraid that it might be a hardware issue. Is it possible I damaged something on the shield when cutting the power and current measurement jumpers.

If so any ideas what should I try to check on the shield?

2

Swap the two motors (with the power OFF) and see if the problem moves with the motor.

Triple check all connections for continuity or shorts to neighboring terminals. Check all voltages.

3

Thanks for the reply.

I just swapped the two motors. Motor B again (physically the other motor) rotates only when direction is set to HIGH.

Led on B is not flashing and measuring the voltage on the motor B output is 0.

I also tried to do some more measurements on the motor shield.

I disconnected the motor power supply and measured the voltage difference between pins on L298
using the schematic provided for the shield (Schematic)
When setting speed to 250 the voltage between DIRA and DIRA# is 4.7 or -4.7 depending on direction
However for motor b DIRB and DIRB# is 4.7 or 0

So i think the nor gate is between brake and direction pins for motor B is broken...