Pinpoint PH monitor

[Lampshade]

Hi, i've had a PH monitor kicking around for awhile that had a bad probe. I went out and bought a new probe recently and can't get it to calibrate. I'm using the 7 and 10 solutions, and in the 7 i can read 7, but in the 10 the highest reading i can get is 8.15, even if i adjust the 7.0 calibration aswell as the 4-10. Can the monitor itself go bad? The battery's fairly new, used it in a stud finder for a bit, but should be near new. Anyone else have this problem?