Are the two converter boxes the same make and model? If not, you probably have your answer. All converters were not made equal. The digital tuner in one box might not be of the same quality as the digital tuner in another, making it more difficult to pull in all available channels.

On the TV that gets fewer stations, make sure the antenna is connected securely to the converter box and that there is no damage to the antenna cable at all. Even a slight bend or fray can disrupt signal quality.

Is the antenna cable that runs to the box significantly longer than the cable running to the box that receives more stations? The longer it is, the worse reception can get.