Dude,just buy a new one. They are like $40.they get inaccurate after about a year anyhow, as the sensor gets used up and dipping it into chemicals, etc. . .It sounds like water got into it. It has a micro processor that handles the calculations and sends it to the screen. The rest is just the sensor and wiring and chipboard/battery. Its a simple device. the fact that is still semi-works is promising, but if its all wired up correctly assuming you put it back together properly - it should work. If it was short circuited, it would show 99.9 on the screen or something like that.... so thats not it.Do you have a multimeter? Set it to the voltage of the battery (1.5 x 2 = 3v) and touch the red and black terminals onto each component inside. IT will show electric current through each component to rule out which one is faulty. Part by part until you find something that isn't passing current or not the right current - Then you remove that part and replace it (good luck finding parts)All this work to save $40. ? Cheap ass - LOL just kidding .  I got a ph tester too. Enough said about that hehe.