A repeater for a communication network having an isolation circuit for disabling the transmission of a fault-indicative signal through the repeater onto the network. A retriggerable one-shot starts timing with high to low signal transition. In the absence of a second transition within a defined time period, the one-shot triggers a flip-flop which, depending on the logic level of the input signal, generates an enabling signal passed to a logic gate to selectively allow and cut off the transmission of the signal to the repeater circuit input.