Abstract: Isolation of a wired-OR fault on a printed circuit board is accomplished by first powering up the circuit board, then injecting a short pulse on the common buss and detecting the current flow by use of a ferrite core. The ferrite core is sufficiently small that it can be moved about the circuit board to the terminals of the various components that are connected to the current buss in a wired-OR configuration. The change of inductance created by the magnetic field associated current pulse flowing through the terminal of a component sinking the current creates a ringing effect which is amplified and compared against a reference voltage. The output of the comparator circuit is used to create a fault alarm signal.