hi, I have had my line 6 spider iv 75 amp for about 8 months and only recently this problem occurred. all of the knobs don't turn all the way up for example i cant get the green hi gain, metal or insane amp models or pitch tremolo or sweep echo effects, i can rotate the knobs all the way but it doesn't recognize the last third of the rotation for any, I can not find a solution and a factory reset don't work, any ideas?