A device for measuring and isolating noise-creating imbalances in a paired telecommunications line has an internal circuit. The internal circuit includes a pulse generator. Pulses provided by the pulse generator are applied to an interface which includes balanced pathways to the conductors. The pulses are applied simplex (longitudinally) to the pair of conductors. Upon encountering a fault in the pair, a reflected metallic voltage signal is received by the interface. The reflected metallic voltage signal is sampled by an analog-to-digital converter. Data relating to the sampled signal is displayed for detection and location of faults on the pair.