Open the line controller enclosure, found that the inner very dirty, solder joint and metallized hole has black, remove the liquid display screen and hair plate, found that provide the latter with the driving voltage contact also is full of green rust and black sludge, then take out a small circuit board, with anhydrous alcohol swab repeatedly each contact, solder joints, until clean as new; Rinse again the volume potentiometer, after waiting for alcohol volatilization of commissioning, blue light is normal, the volume has no noise.YpKservice manual download site