Sounds like you have something wrong with the Optical Sensor, which is situated in the base. That sensor senses a rotation of the Ball Feed Gear. Each rotation of that gear equates to one ball thrown out. If the sensor is bad, the sensor tag is missing from the bottom of the gear, or there is dust or dirt between the tag and the sensor, ball feed will operate at only one frequency, regardless of what the Ball/Min control is set at. If the problem is simply dust between the sensor and tag, sometimes you can get the robot working again by blowing compressed air in through the access slot in the bottom of the base and directing it at the gear, dislodging the dust and allowing the sensor to once again sense the tag. Otherwise, you will need to remove the Base Top from the Base Bottom (16 screws) and check that the wires to the sensor look good, that the tag is still mounted on the bottom of the gear, and remove any dust/dirt in the base. Very rarely, the sensor itself may be bad, and needs to be replaced, but that typically only happens with much older units, not brand new ones.
The only thing I have ever found that causes double throws is the head height being adjusted incorrectly. One of the 4 rings painted on the Upper Ball Tube must be right at the top of the Lower Ball Tube. Otherwise, balls won't stack up correctly inside the ball channel so the top ball is positioned properly to be pushed into the wheels, grabbed, and thrown forward.
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