[codefox1]

Well, you could just splice in a known good one to the three contacts and see if you restore functionality. If you do, the old one is open at some point. Or when the set is off, you could use an ohm-meter to see if the wiper (center tab) has continuity and goes up and down in resistance as you turn the knob. Check in terms of both the outer tabs, as the break could be anywhere. If it is not that, then check back with us.