Examples of a Dc Circuit Fault Isolation Procedures-CONT.

TM 11-5895-1012-10

the fault has been isolated.

The Technical Controller then actuates the cut-key of

(2) Upon isolation of the fault at a distant station,

the receive channel on the dc equal level patch panel.

the responsible Technical Controller should coordinate

If a cut-key is not available, the Technical Controller

efforts to restore service to the subscriber. The tempo-

inserts a dummy plug into the receive channel jack ap-

rary transfer of the circuit to a spare channel may be

pearance at the dc equal level patch panel. This action

required.

applies hold battery current to the loop, which pre-

(3) Upon notification that the necessary repairs

vents the receive equipment from running open. The

have been made, the responsible Technical Controller

Technical Controller can then proceed with the follow-

should assist the distant Technical Controller(s) in the

ing fault isolation procedure to determine if the fault

restoration of normal service to the subscriber.

exists in the VFCT channel equipment, either in the lo=

(4) Complete station records in accordance with

cal station or at a distant terminal.

established procedures.

(1) Consult the station circuit files and identify

d. Channel Degradation. The local Technical Con-

the voice frequency and tone channel assignments of

trol Facility is notified by a connected subscriber that

the dc subscriber circuit which is in trouble.

a teletypewriter machine has started to produce

(2) Place the selector switch of the teletype carrier

garbled page copy. The report states that the error rate

test set to the designated tone channel, and connect

is serious enough to render incoming messages unintel-

the unit to the voice frequency equal level patch panel

ligible. The local Technical Controller should proceed

LINE transmit jack serving that channel of the VFCT

as follows:

equipment.

(1) Subscriber Loop Check. The local Technical

(3) Patch the dc output of the VFCT terminal at

Controller should patch a monitor teleprinter into a

the dc equal level patch panel to a distortion analyzer,

MONITOR jack appearance of the complaining sub

distortion test set or a monitor teleprinter. Jack ap-

scriber receive channel at the primary dc patch panel

pearances for these items of equipment appear on the

to determine the quality of the signals passing through

miscellaneous/interbay jackfields of the dc test bays. If

to the subscriber loop. An alternate method is to patch

teletype signals are not received at this point, a failure

a distortion analyzer into the subscriber circuit at this

in the local VFCT channel equipment is indicated. If

point to determine the type of distortion causing the

the VFCT passes the test signal, then the fault lies in

signal degradation. This information is most useful in

the voice frequency area or at the distant terminal (c

many instances in identifying the origin of a fault con-

below).

dition. Illustrations of normal and distorted teletype

(4) If the local VFCT equipment fails the test in

signals are contained in the instruction manual for the

(3) above, request that station maintenance personnel

distortion analyzer.

check the VFCT channel equipment serving the sub

(2) Range Setting Check. If the telegraph signals

scriber loop.

are copied without garbling during the subscriber loop

(5) The local Technical Controller should coordi-

check, the reported fault condition may be caused by

nate the transfer of the subscriber circuit to a spare

channel, if necessary with the distant station Techni-

an improper range setting of the subscriber teletype

machine and this should be checked. If the copy is

cal Controller.

(6) Upon correction of the fault, the local Techni-

garbled proceed to (3) below:

cal Controller should take action to return the sub

(a) Request the subscriber to standby for a test

scriber circuit to its normal routing. To prevent un-

transmisssion to evaluate the adjustment of the tele-

necessary loss of traffic on the circuit, the patchcords

type machine.

at both ends of the circuit should be removed simul-

(b) Patch a pattern generator output into the

taneously.

LINE jack appearance of the subscribers receive cir-

(7) Complete station records in accordance with

cuit (transmit from the TCF to the subscriber) at the

establishedprocedures.

primary dc patch panel. Transmit a Fox test message

c. Failure at Distant Terminal. If signals are detect-

to the subscriber station. The range control of the sub

ed during the test in b(3) above, and the local voice fre-

scriber teletypewriter machine should be adjusted by

quency channel equipment serving the VFCT check

maintenance personnel to the midpoint of the range

good, a failure in the VFCT at the distant station is in-

over which perfect page copy is obtained.

dicated. The local Technical Controller should do the

(c) Upon correction of the fault, complete sta-

following:

tion records in accordance with established proce-

(1) Contact the Technical Control Facility at the

dures.

distant VFCT terminal and request that he continue

(3) DLIU Check. If the monitor teleprinter pro-

the fault isolation procedure through the distant sta-

duces garbled page copy when patched into the sub

tion. This procedure must be continued by all Techni-

scriber circuit, the Digital Line Interface Unit should

cal Control Facilities involved with the circuit until

be checked for faulty operation. The Technical Con-

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