Wait, 0 V from the tuning potentiometer too? You’d need a bit over 3.3 V to hit midi note 0 and about 5 V to hit the lowest note on a piano, so if you don’t get any voltage from the tuning pot at all, your keyboard may have trouble getting something useful out of the oscillator. Double-check how the tuning pot(s) are wired up.
But this could just be that the 3340 is fried; if the summing node is completely dead and your tuning pot is wired up in series with the 100k instead of as a voltage divider (see here for some discussion of various way to wire it), the current has nowhere to go.