I'm fixing this guitar for a friend of mine. It has active pickups, a Fishman piezo bridge with the Fishman preamp. Some other guy wired the battery ground and the pre output to the ring lug of the output jack, so the battery was discharging even when the guitar was unplugged.
At first i erroneously put the piezo output on the sleeve, thinking it was a ground; i tried in other ways (both bare and battery ground to the sleeve, pup output to the tip and piezo to the ring and viceversa etc) but in the end the result is the same, even after putting it back to the old configuration: the piezo doesn't work.
And what's worse i can find schematics for the fishman, but they have nothing to do with what's on the guitar, and i can't find the guitar's diagrams. If there's any knowledgeable folk out there who's willing to lend a hand i'd gladly take it.
I should note that i disassembled the bridge to see how it was made; but after putting it back together everything seems in order, as there's continuity between the saddles and the piezo input on the preamp.
One weird thing: when testing the output jack, i plugged a mono jack in; i got continuity on ring and sleeve, but on the tip instead i got resistance. What could it be? Just bad soldering?