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Page Title: Examples of DC Circuit Fault Isolation Procedures-CONT.
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TM 11-5895-878-14&P
Patch Bay.
(6) Upon correcting of the defective channel
(d) Notify both the subscriber and the
equipment, he should coordinate with the distant VFCT
distant VFCT technical controller that the circuit is ready
terminal to return the subscriber circuit to the normal
for the passing of traffic.
VFCT tone channel by simultaneously removing the
patchcords at both stations (if a spare channel has been
(e) Complete station records, trouble
used).
reports and log entries.
(7) Complete station records, trouble reports,
(4) Defective subscriber terminal equipment.
and' log entries.
The station Technical Control activity is notified by
maintenance personnel that an electrical failure has
c. Failure at Distant Terminal.  If no signals are
occurred in the page printer at the subscriber terminal.
detected during the check in b(2) above, a failure in the
The station technical controller should:
VFCT system at a distant station is indicated.  The
station technical controller should:
(a) Insert a dummy plug in the line jack
appearance of the subscriber's receive channel at the
(1) Contact the technical controller at the
DC Patch bay to isolate the subscriber loop from the in-
distant VFCT terminal through the orderwire and request
station circuitry.
that he continue the fault isolation procedure through his
station. This procedure should be continued by all
(b) Upon notification by maintenance
technical controllers involved until the fault has been
personnel that the equipment failure has been corrected,
isolated.
he should remove the dummy plug from the line jack
appearance in the Patch bay to restore the subscriber
(2) Upon isolation of the fault at a distant
loop to the in-station circuitry.
station, and as requested by the responsible controller,
he should coordinate efforts to restore service to the
(c) Perform a Fox test as required, to
subscriber. This may involve a temporary transfer to a
ascertain that the printer is properly adjusted.
spare channel.
(d) Complete stations records, trouble
(3) Upon  notification  that  the  necessary
reports, and log entries.
repairs have been made, he should assist the distant
b. Defective VFCT Channel Equipment.
The
technical controller(s) in the restoration of normal
Technical Control activity is notified by a connected
service to the subscriber.
subscriber that service appears to have been interrupted
(4) Complete station records, trouble reports,
on his receive circuit. The technical controller initiates
and log entries.
his fault isolation procedures. A zero reading is shown
when a voltmeter is inserted in a monitor jack of the
d. Channel Degradation.  The Technical Control
subscriber receive channel at the DC, (low level) patch
activity is notified by a connected subscriber that a
bay. The station technical controller then actuates the
teletypewriter machine has started to produce garbled
cut-key (if available, if not, inserts a dummy plug) of the
page copy.  The report states that the error rate is
receive channel at the DC bay to apply hold battery to
serious enough to render incoming messages largely
the loop. To determine if a fault exists in the VFCT
unintelligible.
channel equipment, either in the station or at a distant
(1) Subscriber loop check.
The station
terminal, the station technical controller should:
technical controller, upon receipt of this fault notification,
(1) Consult the station circuit file and identify
should patch a monitor Teleprinter into a MONITOR jack
the voice frequency (VF) and tone channel assignments
appearance of the subscriber receive channel at the DC
of the DC subscriber circuit.
Patch bay to determine the quality of the signals passing
through the subscriber loop.  (As an alternative, the
(2) Place the selector switch of the Teletype
technical controller may patch a Distortion Analyzer into
Carrier Test Set to the designated tone channel, and
the subscriber circuit at this point to determine the type
connect the unit to the V]F Patch bay "LINE TRANS"
of distortion causing the signal degradation).  This
jack serving that channel of the VFCT terminal.
information is most useful in many instances in
(3) Patch the DC output of the VFCT at the
identifying the origin of a fault condition. Illustrations of
DC Patch bay either to the Distortion Analyzer Set,
normal and distorted teletype signals are contained in
Distortion Test Set or to a Monitor Teleprinter. The jack
the instruction manual for the Distortion Analyzer.
appearances are located in. the MISC/INT jackfields of
(2) Range setting check.  If the telegraph
the DC test bays. If teletype signals are not received at
signals are copied without garbling during the subscriber
this point, a failure in the station VFCT channel
loop check, the reported fault condition may be caused
equipment is indicated.  If the VFCT passes the test
by an improper range setting of the subscriber teletype
signal, then the fault lies in the VF area or distant
machine and this should be checked.  The station
terminal (refer to c below).
technical controller should:
(4) Request that station maintenance check
(a) Request the subscriber to stand by
the VFCT channel equipment serving the subscriber
for a test transmission to evaluate the adjustment of his
loop.
teletype machine.
(5) The technical controller should call the
distant VFCT terminal and coordinate the transfer of the
subscriber circuit to a spare channel (para 3-8) if
required, because of anticipated circuit outage.
3-12

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