Abstract: Sensors SE and actuators AT electrically linked to groups of circuit components to be monitored, e.g. in a central office of a telephone system, are connected to a preprocessor, interfacing them with a microprocessor, which detects an incoming request signal from any group and, after evaluation, sends it on to the microprocessor, causing the latter to emit a confirmation signal which the preprocessor transmits to the corrsponding group actuator. A component-identification signal received from that group and evaluated by the preprocessor is then forwarded to the microprocessor which thereupon, through the preprocessor, instructs the corresponding component actuator to send out an enabling signal to the component thus identified. A response by that component, in the form of an error signal, also undergoes evaluation in the preprocessor and is then passed on to the microprocessor where it is classified and read out to a printer.