[TowerTalk] Issue with HyGain control nox

[cqtestk4xs at aol.com]

I'm going through my rotor collection getting ready to sell them and found an issue with two of the control boxes.  Using a good T2X as the rotor I got normal operation and indication from several control boxes.  However, two other control boxes did not operate as they should.  Both boxes operate normally except indication is off.  One has indication stopping at 90 degrees even with the calibrate turned full clockwise.  The other does not indicate the other way past 270 degrees even with the calibrate turned full counter-clockwise.  Both however, do rotate the rotator 360 degrees.
I know the rotator is indicating OK since it indicates perfectly with three other control boxes.  Any ideas as to what is going on?  My first thought is the calibrate pot is bad, but I'm not sure. 
Bill K4XS/KH7XS