Testing checklists and troubleshooting
This domain tests disciplined test execution and fault isolation. The exam expects a repeatable checklist: confirm fiber type and connectors, inspect and clean, verify wavelength and reference, test to the correct standard, and document results. Troubleshooting should narrow the fault by measurement, not by guessing.
Pre-test checklist
Confirm single-mode versus multimode, core size, connector polish (UPC/APC), wavelength, test standard, reference method, and required directions. Verify calibration dates and battery state. Inspect and clean every endface before referencing. Use known-good reference cords and adapters. Record source power, meter readings, wavelength, instrument serial numbers, and test conditions. For multimode, confirm the mandrel wrap; for single-mode, confirm the correct launch condition and any required bidirectional averaging.
Troubleshooting flow
If a link fails its budget, first verify the reference and inspect/clean both ends. Then check polarity, port mapping, and connector mating. Use an OTDR or VFL to divide the link: a high-loss event near one end points to a connector or patch panel; distributed slope suggests fiber damage or macrobends; no light suggests a break, wrong port, or transmitter issue. Re-test after every corrective action rather than assuming the fix worked.
Worked example
A 850 nm multimode link measures 2.6 dB against a 2.0 dB budget. The reference is rechecked at 0.00 dB. Inspection finds a dirty adapter at the midpoint patch panel. After cleaning, the link measures 1.7 dB and passes. The OTDR is not needed because the checklist isolated a connector fault. If cleaning had not helped, an OTDR event table would locate the next suspect.
Traps
- Skipping endface inspection because the connectors are new.
- Referencing with a dirty cord and then trusting the result.
- Testing at the wrong wavelength or with the wrong fiber type setting.
- Replacing cable before checking adapters and polarity.
- Failing to document the before-and-after readings.