A method for determining sources of interference that cause partial discharges in an encapsulated conductor structure of a magnetic resonance apparatus, particularly in a gradient coil. Under the method, a low-frequency high voltage is applied to a conductor, and signals resulting from an adjacent high voltage are measured within a frequency range located in the kHz range, particularly from 40 to 400 kHz. The signals are analyzed in order to determine partial discharges. The conductor is again charged with a low-frequency high voltage and additional signals are measured within a frequency range located in the MHz range, particularly from 10 to 300 MHz. The additional signals are analyzed in order to determine partial discharges.