Hi
I have had problems with my American JTV 69....the B string piezo started to become intermittent ,
when I investigated, the wire from the pickup to the board broke away from the board as soon as I touched it...
I cleaned the wire and desoldered...Job done.
Today while playing the D string went dull...then intermittent. Started to investigate once again....the pickup wire
was firmly attached to the board so I unsoldered it then resoldered....job done again.
This is just to say that you may not need to replace a piezo pickup....it may be just a dry joint.
Hope this helps
Mike