Examples of DC Circuit Fault Isolation Procedures-CONT.

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

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.

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