Abstract: A fixture is provided for locating open conditions within circuits and short conditions between adjacent circuits on a flexible substrate having circuits extending along each side, as well as individual circuits extending along both sides. In one station of the fixture, the flexible circuit extends against a conductive backing plate, and conductivity measurements, to detect open conditions, are made between two probes moving among test points on the first side of the substrate, which is opposite the backing plate, and between one of these probes and the conductive backing plate. The latter type of measurement is used particularly to detect an open condition in a via extending through the substrate.