VOLT DROP measurements. Repeat for BA direction
3-7. Testing Cable, Special Purpose,
After faults have been sectionalized between two at-
(7) Request the attended points to apply pcm
traffic. If the fault is a short or an open, traffic may be
tended points in an overall system, the AN/PTM-7
applied by operating the TD-204/U or TD-754/G
may be used to further localize and isolate the fault
within one of the links by performing loopback
NOR OPR-ZERO SET-READ switch to READ. If a
measurements (a below) and bridging measurements
defective TD-206/G is at fault, the pcm should be the
normal traffic from a TD-352/U or TD-353/U at the
(b below). Troubleshooting by looping back is also
effective for locating a defective TD-206/G which still
appears to have an output. This type of fault usually
(8) Check the PCM IN, PCM OUT, and VOLT
DROP measurements in both directions. The attended
shows up as loss of framing on the TD-352/U or
TD-353/U, or as noise or clicks on all audio charnels.
points should both receive their respective looped-back
a. Loopback Measurements. Loopback measure-
pcm traffic, although one point will have an incorrect
returned signal due to the fault.
ments are used to check link continuity and to ac-
curately localize opens and shorts in the link. Dc cable
Example: If the fault is a shorted CX-4245/G, the
receive cable current (rcc) at the TD-204/U or
current and pcm traffic are routed through the
TD-754/G will be low.
TD-206/G and returned to the attended point from
which they originated. During loopback checks, at-
If the fault is a defective TD-206/G the TD-352/U or
tended-point operators can talk only as far as the
TD-353/U at the attended point will either be out of
frame or have noise or clicks on a audio channels.
AN/PTM-7. The procedure for performing a loopback
check is described in (1) through (8) below:
Thus, the fault is on that side of the TS-1323/PTM-7
that is receiving an incorrect looped-back signal.
It is assumed that the lineman travels from
b. Bridge-Circuit Measurements. Bridge-circuit
the west attended point in the following dis-
measurements are used to locate opens and shorts in
the CX-4245/G at distances up to 1 mile. Before per-
forming bridge-circuit measurements, both the nature
(1) Proceed to the first TD-206/G west of the
of the fault (open or short) and the link in which the
(2) Connect the TS-1323/PTM-7 to the
fault exists should have been determined in accordance
TD-206/G and both CX-4245/G's as shown in figure
with the loopback check procedure described in a
above. If a shorted CX-4245/G is suspected, proceed
as described in (1) below. If an open CX-4245/G is
(3) Operate the OPERATION SWITCH to
suspected, proceed as described in (2) below.
(4) Signal the east attended point. If an open cir-
cuit or low-resistance short exists, it should not be
Be sure cable power is removed before per-
possible to signal or communicate with the east at-
forming these tests.
tended point. If a high-resistance short exists, it may be
(1) Short-circuit checks.
possible to signal and communicate with the east at-
(a) Connect the suspected CX-4245/G to the
(5) Request the west and, if possible, the east at-
(b) Pull out the BATTERY POWER switch;
tended points to finish dc cable current, with the
operate the CAP-RES switch to RES and the METER
SELECT switch to BRIDGE.
TD-204/U or TD-754/G NOR OPR-ZERO SET-
READ switch operated to ZERO SET.
(c) Depress and hold the READ switch. Slowly
(6) Operate the TS-1323/PTM-7 DIRECTION
adjust the DISTANCE TO FAULT control until the
switch to AB and check DC VOLTS, DC AMPS, and
TEST METER indicates zero (or null).