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Page Title: Examples of a Dc Circuit Fault Isolation Procedures-CONT.
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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
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:
(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-
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
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
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-
tion records in accordance with established proce-
(1) Contact the Technical Control Facility at the
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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