"chopper" modules are either a large transistor
or a bank of FET's on a heatsink
they "chop" the motor voltage creating the PWM to control motor speed
they probably failed open (fried)
some trucks they are external others they are internal (in the card)
i would assume for steering they would be in the steer card
i dont know this machine but i would try to track the steer motor cables back to its controller
id also go get the book if it was me
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