10
Using the Test Set for Troubleshooting Circuits
Some general troubleshooting procedures and tips are provided here. These procedures may require
other tools or equipment that are specific to the communications system installation trade. For a
complete selection of VDV (Voice-Data-Video) tools, please refer to a Greenlee full-line catalog or visit
our website at www.greenlee.com.
RFI (radio frequency
interference)
Split pair
An unbalanced pair near a radio transmitter will
be prone to RFI. Adding radio filters can reduce the
interference on the line (the symptom), but does not
solve the imbalance (the problem). To troubleshoot,
break the circuit down into sections and check each
section for split pairs or a resistive imbalance.
Improperly removed bridge taps may also introduce
RFI. Bridge taps, which were once used for party-
line service (multiple users sharing a cable pair),
were often disconnected but left in place, with
a stub section of cable still connected. This stub
section can act as an antenna and induce radio
signals into the circuit.
Ground fault
Check for the presence of AC line voltage. If AC line
voltage is present, measure the level. If it is typical
line voltage, contact the local electric utility.
A long run of telephone
cable near a power line
Contact the local electric utility.
Power hum
Cable imbalance
Break the circuit down into sections and check each
section for an imbalance.
Momentary or impulse
noise
This may be due to an unbalanced cable, nearby
power switch gear, or similar equipment.
Popping, crackling
The customer has an older carbon transmitter type
of telephone.
Noise
Hiss (white noise);
pulse dialing causes a
momentary change in the
sound of the noise
This is probably due to water in the cables.
Cross connection
Direct wiring fault
Check for crossed pairs.
Cross-talk
Split pair
A split pair (a circuit made up of wires from two
separate wire pairs) will be unbalanced and prone
to cross-talk.
Constant ringing
Telephone wire in
contact with an AC
power line
This is a potentially hazardous situation!
Remove the test set from the line carefully and
immediately.
Symptom*
Possible Cause /
Troubleshooting Step
Explanation
* Wet cables may cause most of these symptoms and may cause multiple symptoms to appear at
the same time.
