A VFL is used to detect faults, breaks, or bends in fiber optic cables by emitting a bright red light that is visible even through the fiber's jacket. There are no specific requirements for this document. This includes Doppler. Fiber connection issues may arise from misalignment of patch cords with device interfaces, or mismatch of fiber types between pigtail, patch cord, and coupler. The RJ45 interface is not connected correctly to. When the Status light is red, you can use a PC super terminal to confirm whether the switch's software is running normally. S3100 SERIES SWITCHES TROUBLESHOOTING GUIDE. Visual fault locator cable continuity tester locates fibers, finds faults, verifies continuity and polarity.