Circuit assembly for cable checking, cable testing, cable diagnosis and/or cable fault localisation in conjunction with a cable, comprising - a voltage source having a first voltage multiplier for a positive voltage and a second voltage multiplier for a negative voltage, - a protective resistor, - a voltage divider, - interconnected current sources (2, 3) in conjunction with the voltage multipliers (13, 14) for generating a test voltage across the load impedance of the cable in order to charge and discharge the load capacity of the cable, the interconnected current sources (2, 3) being connected to the cable and to the voltage divider via the protective resistor, and - a controller coupled to the voltage source and to the current sources (2, 3), characterised in that the controller has a digital signal processor for controlling the test voltage across the load impedance of the cable, which voltage is measured across the voltage divider, and for specifying the target value of the voltage source, in that the voltage multipliers (13, 14) are connected either to two main converters (10a, 10b) or to a main converter and an auxiliary converter that generates a positive and a negative auxiliary voltage, such that either a positive voltage corresponding to the target value specification and a constant, uncontrolled negative voltage or a negative voltage corresponding to the target value specification and a constant, uncontrolled positive voltage are applied to the outputs of the voltage multipliers (13, 14), the particular uncontrolled voltage being generated either by the respective main converters (10a, 10b) or by the uncontrolled auxiliary converter, in that the voltage multipliers (13, 14) are coupled to the current sources (2, 3) via a coupling diode (8, 9) in each case, such that rearward powering of the voltage multipliers (13, 14) is prevented, in that the interconnected current sources (2, 3) are connected to the voltage divider and to the cable via at least one protective resistor, and in that the two interconnected reference potentials of the voltage multipliers (13, 14) are connected to the reference potential of the cable via a measurement impedance that can be adapted to the measurement region, the reference potentials of the voltage multipliers (13, 14) and the reference potential of the voltage divider being an auxiliary earth. - a voltage source having a first voltage multiplier for a positive voltage and a second voltage multiplier for a negative voltage, - a protective resistor, - a voltage divider, - interconnected current sources (2, 3) in conjunction with the voltage multipliers (13, 14) for generating a test voltage across the load impedance of the cable in order to charge and discharge the load capacity of the cable, the interconnected current sources (2, 3) being connected to the cable and to the voltage divider via the protective resistor, and - a controller coupled to the voltage source and to the current sources (2, 3), characterised in that the controller has a digital signal processor for controlling the test voltage across the load impedance of the cable, which voltage is measured across the voltage divider, and for specifying the target value of the voltage source, in that the voltage multipliers (13, 14) are connected either to two main converters (10a, 10b) or to a main converter and an auxiliary converter that generates a positive and a negative auxiliary voltage, such that either a positive voltage corresponding to the target value specification and a constant, uncontrolled negative voltage or a negative voltage corresponding to the target value specification and a constant, uncontrolled positive voltage are applied to the outputs of the voltage multipliers (13, 14), the particular uncontrolled voltage being generated either by the respective main converters (10a, 10b) or by the uncontrolled auxiliary converter, in that the voltage multipliers (13, 14) are coupled to the current sources (2, 3) via a coupling diode (8, 9) in each case, such that rearward powering of the voltage multipliers (13, 14) is prevented, in that the interconnected current sources (2, 3) are connected to the voltage divider and to the cable via at least one protective resistor, and in that the two interconnected reference potentials of the voltage multipliers (13, 14) are connected to the reference potential of the cable via a measurement impedance that can be adapted to the measurement region, the reference potentials of the voltage multipliers (13, 14) and the reference potential of the voltage divider being an auxiliary earth.