Casio CZ/ VZ/ FZ - Pro Series

>I tested the voltage between the first and second pins, and it stays at
>1.20 nearly all the time, but sometimes it drops to 1.00 or raises until
>1.25, and when this happens the sound changes the pitch. When the sound
>is at 1.25 (about one semitone up) I can't use the pitch bend to raise
>it even more, I can only lower it some semitones. I bet this means a bad
>potentiometer, or a bad voltage coming into it. I'll try to buy another
>one, it's a 618k audio pot, am I right? I still haven't tested the third
>pin because the random nature of the problem, but I'm at it.

You should measure with respect to ground.  The typical configuration for 
pitch/mod wheels is that the potentiometer goes between the positive and 
negative supply voltages (or positive and ground), and the wiper (middle 
terminal) goes to an ADC.  The potentiometer here acts as a voltage divider 
and the voltage at the wiper terminal varies from one supply voltage to the 
other (or whatever it's connected to).