A technician's guide to fiber optic troubleshooting: diagnose signal loss, connector, splice, bend, and return-loss issues — with OTDR steps to fix each. When issues like signal loss, slow speeds, or intermittent connectivity arise, systematic troubleshooting is key. These high-speed, high-capacity communication networks are increasingly replacing copper cables, offering superior performance and. This document describes how to troubleshoot fiber optic interfaces by addressing some of the fiber optic module and cabling specifications. The information in this document is based on all Catalyst 9000 Series switches. Many fiber internet problems come from dirty connectors or loose plugs, not major faults. Power. Fiber optic networks are generally reliable, but like any technology, they can experience problems that affect performance.