An instrument for detecting and indicating the locations of pinholes and fractures in non-conductive coatings (paints, linings, films, porcelain, enamel, coal tar, asphalt, etc.) that are applied to a metal surface. Completely transistorized, low frequency electrical pulse generator assures efficient detections with no harm to the coatings. They also permit indirect grounding. Output voltages are variable as desired and readable on built-in meters. Units are housed in portable dust and moisture proof PVC sturdy cases.