SMS122 question


I bought a brand new SMS-122 PH controller 2 months ago for my Ca reactor. The calibration process went fine and it was working good. Now when I went to recalibrate it with pH7 and pH4 standards, the back trimmer is completely turned and will not go below 4.1. I am guessing, something is wrong with my probe! And if it is the probe, has anyone tried to fix this problem by recharging it in concentrated HCl!

Any comments/suggestions welcome!