The invention relates to the field of magnetic resonance, and in particular to determining a location of an error in a supply or signal line (12). Due to the rugged environment for MR systems (10) in hospitals supply or signal lines (12) of MR systems (10) are error prone. For serviceability and part replacement it is important to locate the error in the supply or signal line (12) or to identify the subunit (14, 16, 18, 20) of the supply or signal line (12) in which the error occurred. The basic idea of the invention is to use an additional impedance (24), that is coupled to the supply or signal line (12) of the MR system (10) in the region of interconnection (22) for locating the error in the supply or signal line (12). The additional impedance provides a reference impedance value. By measuring the impedance and comparing the measured impedance to the reference impedance value, the error in the supply or signal line (12) can be located. In one embodiment the additional impedance (24) is realized as additional capacitance and provided as a capacitor (28).