Re: TETRIX servo not returning correct value
As long as the servo is responding to your input, it is likely wired correctly even if it does not act as you expect.
Looking at your code, it seems possible that that servo target is being set and incremented rapidly as the program loops. Have you noticed the servo moving further depending on how quickly you release the button on the joystick? It only takes a second for the code to loop many, many times. If this is the case, you may need to add some sort of wait/timer when manually incrementing/decrementing.
Lastly, your code has no limits set to prevent the servo from rotating its full degree of movement. This may be what you want, but generally you want a servo to only move between two specific points that are within the full range. Below is some sample code similar to yours but with an added range check for safety. You just change the value of the two constants to set the correct limits.