Emergency Restoration - Troubleshooting the Problem
There are several reasons for all or any part of a system to ‘go dark.’ The reason may be obvious, such as a falling
tree shearing a span. More often than not, the reasons may not be that apparent. The first step in restoration is to
determine exactly what and where the problem is located. The methodical approach described below is the wisest
way to determine the cause of the outage. All records of installation parameters should be easily available:
Check the Transmitter - Measure the transmitter output at the output connector with an optical
power meter. Check the received power to that recorded at installation.
Check Patchcords at the Transmitter End - Patchcords, connectors and sleeves may be damaged
or defective. Replace suspect patchcords with known good ones and measure the output power
compared to installed values.
Check Patchcords at the Receiver End - Repeat the process above at the far end of the system.
Replace suspect patchcords with known good ones and measure the output power compared to
installed values. If the power is within prescribed limits, the problem is in the receiver.
Check the Cable Plant - This can be done from either end of the system with an OTDR. Compare
the OTDR trace with the as-built documentation. This will often show you to within a few yards
where the problem might be.
Unfortunately, many problems turn out to be a catastrophic failure of the cable. Common causes
include rodent damage, lightning strikes, trees falling on the cable, traffic accidents, gunshots or
other vandalism. Mechanical causes could be freezing water in conduit, failed splices or environmental
damage within a splice closure. In many cases, a short span of cable may need to be replaced quickly
to restore service.