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7.10 Tow Cable Troubleshooting
Historically, most system problems occur in the tow cable and their connectors. Before proceeding, verify
cable continuity from the shipboard end of the cable to the towfish. The presence of a shorted or open
wire in a tow cable can be determined by using a multi-meter. An open or shorted wire can be located
using the techniques described in the following subsections.
7.10.1.1 Shorted Wire
The following procedure may be used to approximate the distance to a single short or a point of high
leakage between a conductor pair or from a conductor to a shield.
1. Disconnect both cable ends.
2. Short the two connector pins (or wires if un-terminated) of the shorted pair at both ends and
measure the total resistance between the ends.
R1 + R2 =_______________
3. Remove the shorts.
4. Measure the resistance between a shorted pair on one end with an ohmmeter on the Rx1 scale.
R1 + Rs =_______________
5. Measure the resistance from the other end.
R2 + Rs =_______________
6. Add the measurements of
STEP 4 and STEP 5. Subtract the measurement of STEP 2, and divide the
result by 2.
Rs =_________________
7. Subtract the value of 6) from the measured values of 4) and 5).
R1 =_________________
R2 =_________________
8. The distance to the short from end #1 is the ratio of (R1/R1+R2) times the total cable length.
Recheck from end #2, which is (R2/R1+R2) times the cable length.
7.10.1.2 Open Wire
An open wire in a cable is much more difficult to locate than a short circuit. Therefore, a capacitance
bridge is recommended. Measuring the capacitance from the open wire to the shield on both ends allows
two different capacitance readings to be recorded. This represents a direct ratio related to cable length
and distance of break from each end. Before cutting the cable, double-check the same ratio of capacitance
using an adjacent good wire in a multi-conductor cable. The capacitance may vary from wire to wire,
depending on their separation.
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