The development of the submarine fibre optic cable industry strongly affects communication both globally and regionally. Technology today enables high-quality and fast transmission of various information, and it is evident that underwater cable systems, in relation to the current growth of broadband networks, are still a key determinant of the world's overall telecommunication capabilities and capacities. Considering that more than 90% of the world's electronic communication is carried out via submarine fibre optic cables, it highlights the level of dependence of communications networks on the submarine cable industry, fault detection II and troubleshooting methods. Advances in the submarine fibre optic cable industry are evident, ranging from innovations in cable laying using advanced flowing techniques, to the design of highly advanced, open access submarine cable networks that comprehensively connect all countries within a given area. However, submarine optical cables are exposed to various dangers, from weather to economic activities (fishing and anchoring of ships), which can damage the cables and cause malfunctions. The costs of repairing defects can be high, if the defect is not identified and eliminated in time. In this final paper, the emphasis is on the analysis of procedures for determining and repairing faults on submarine optical cables. Procedures and instruments used for fault testing are described, which enable timely and accurate fault location and testing of the optical submarine cable after repair. In particular, the measurement of the optical signal with the help of the test box during the repair of the fault is presented.