The Electroluminescence (EL) analysis and the current-voltage (I-V) curves determination of PhotoVoltaic (PV) generators are the most used diagnosis methods to check the presence of defects. In the present work, these tests are applied to Interdigitated Back Contact (IBC) PV modules with customizable shape after their manufacturing. A defect is detected in a large number of modules, suggesting an issue related to the semi-automatic manufacturing procedure. Therefore, a detailed analysis is carried out to localize the cause of the defect and a preventive action is proposed in order to reduce the occurrence frequency of the defect during manufacturing.