paolopop, i trust you've already checked the plug between pickup and preamp? most of the problems i've had with alembic instruments lie here.
but i have been able to repair the pickup of an electrum by carefully dremeling (with dental equipment) the pickup (following the cable) until you reach the place the coil is soldered to said cable leading to the preamp connection. i imagine the problem lies here. the coil doesn't often break. a comparably inexpensive fix, you will see.