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Figure 4-92 . Vf subscriber circuit loop-back method, fault isolation flow chart (sheet 2 of 2)
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TM-11-5895-1012-10 Technical Control Facility (General) Manual
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Examples of a Dc Circuit Fault Isolation Procedures-CONT.
TM 11-5895-1012-10
should check the appropriate fuse panel (or associated
a break in the cable between the DCS station and the
alarm output) to verify that no failure has occurred in
subscriber. The report indicates that the cable will be
the loop current distribution system serving the
out-of-service for some period of time. The Technical
subscriber loop and associated DLIU. If, in fact, a
Controller reviews the area circuit records and they
blown fuse alarm is received, the line should be
indicate that an alternate link is not available, or feasi-
checked for a short circuit. If no short is detected, the
ble, between the two communicating locations. Fur
DLIU should be substituted and refused.
ther, it is not practicable to copy the incoming traffic
(2) Open Connection at Subscriber Terminal. If no
at the TCF for use by the subscriber. The Technical
failure in the loop battery supply is detected, the Tech-
Controller should take the following action:
nical Controller should:
(a) Contact the distant Technical Control Facil-
(a) Locate the jack appearances of the sub-
ity and request that traffic be stopped to the sub
scriber circuit at the dc primary patch panel and con-
scriber until the fault has been cleared.
nect a current meter into a monitor jack appearance of
(b) Insert a dummy plug into the line transmit
the transmit circuit (receive circuit of subscriber) to
jack (the subscribers receive circuit from. the TCF) at
measure the loop current.
the dc primary patch panel. This will isolate the sub
(b) If no loop current is observed, connect a
scriber loop from the in-station circuit.
voltmeter into the receive monitor jack appearance of
(c) Upon notification by maintenance personnel
the defective circuit on the dc equal level patch panel.
that the cable has been repaired, the Technical Con-
Measure for a steady mark condition from the VFCT
troller should remove the dummy plug from the line
equipment.
transmit jack at the dc primary patch panel to recon-
(c) If a steady mark condition is obtained,
nect the subscriber loop to the in-station circuit.
substitute the DLIU through patching operations. Per-
(d) Notify both the subscriber and the distant
form the test in (a) above. If no loop current is
TCF that the circuit is ready for the passing of traffic.
(e) Complete station records in accordance with
measured, proceed to(g) below.
(d) If loop current is measured, notify mainte-
established procedures.
nance personnel of the defective DLIU.
(4) Defective Subscriber Terminal Equipment.
(e) Complete station records in accordance with
The Technical Control Facility is notified by main-
tenance personnel that the reason for the open circuit
established procedures.
(f) After maintenance personnel have either re-
condition is an electrical failure in the receiving equip-
paired or replaced the defective DLIU, return the cir-
ment at the subscriber terminal. The Technical Con-
troller should take the following actions:
cuit to its normal routing.
(g) If no loop current was measured in (c) above,
(a) Insert a dummy plug into the line transmit
the TCF interface equipment is not at fault. The break
jack (subscribers receive circuit from the TCF) at the
is somewhere in the dc loop between the station and
dc primary patch panel to isolate the subscriber loop
from the in-station circuit.
the subscriber.
(h) Return the normal interface equipment to
(b) Notify the distant TCF that the circuit is
out-of-service and stop traffic from being transmitted
the circuit by removing the patchcords.
to this subscriber.
(i) Isolate the defective subscriber loop from the
(c) Upon notification by maintenance personnel
in-station circuits by inserting a shorting-type dummy
that the equipment failure has been corrected, the
plug in the line transmit jack on the dc primary patch
Technical Controller should remove the dummy plug
panel.
from the line transmit jack appearance at the dc
(j) Request that user maintenance personnel
primary patch panel to reconnect the subscriber loop
check the continuity of the subscriber loop.
to the in-station circuit.
(k) Upon verification that maintenance per-
(d) Provide a Fox test as required, so that main=
sonnel have located and corrected the fault, insure
tenance personnel can ascertain that the receiving
that the normal TCF interface equipment is connected
equipment is adjusted properly.
to the subscribers circuit.
(e) Complete station records in accordance with
(l) Remove the dummy plug from the line
transmit jack to reconnect the subscriber to the in-sta-
established procedures.
b. Defective VFCT Channel Equipment. The Tech-
tion circuit.
nical Control Facility is notified by a connected sub
(m) Measure the loop current at the dc primary
scriber that service has been interrupted on the receive
patch panel to ensure the circuit is operating normally.
circuit. The Technical Controller initiates fault isola-
(n) Complete station records in accordance with
tion procedures. A zero indication is shown when a
established procedures.
voltmeter is inserted in a monitor jack of the subscrib-
(3) Defective Cable. The Technical Controller is
er receive channel at the dc equal level patch panel.
notified that the reason for the open circuit condition is
4-28

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