I'm trying to calibrate the steering on this unit, in the calibration mode you set the steering pot to center or +/- 0.1 degree. An X at the lower right corner of the screen should change to a green check mark. It will not change to the check mark no matter what I do. I have ohmed the wires and checked voltages multiple times and found no problems. does anyone have any experience with this problem. Any help would be appreciated.