Figure 4-92 . Vf subscriber circuit loop-back method, fault isolation flow chart (sheet 2 of 2)

TM 11-5895-1012-10

that channel's receive circuit on

the reason for the fault and location, and complete sta-

panel at a level of 0 dBm. If the

tion record% in accordance with established pro=

leg of the defective channel has

cedures.

If the level is not correct, the fault has

4-36. Examples of a Dc Circuit Fault Iso-

isolated between the two TCF's and the trouble

lation Procedures

can be turned over to maintenance personnel.

(4) If the tone looped back is received at the

a. Open Circuit Condition. The station Technical

proper level, the distant TCF is requested to remove

Control Facility is notified by a connected telegraph

the loop back patch and the next TCF further toward

subscriber that incoming traffic has been interrupted

the signal source is requested to perform a similar

and that the printer has started to run open.

patch. Again the local TCF inputs a 1000 Hz tone at

Reference to the circuit layout record card indicates

0 dBm and measures the level of the looped back tone.

that the subscriber circuit is connected by cable to a

Following this procedure, trouble can be isolated be-

nearby military installation. The most likely reason

tween any two equal level patch panels in the channel.

for the condition reported is a break in the dc loop

(5) When the fault has been located in the de-

cawed by failure of the loop battery, an open connec-

fective circuit, the tasks is turned over to maintenance

tion at the subscriber terminal, a defect in the cable, or

personnel to clear the trouble. After the fault has been

an electrical failure of the receiving equipment.

(1) Loop Battery Check. The Technical Controller

cleared, restore the circuit to its normal path, obtain

Figure 4-92 . Vf subscriber circuit loop-back method, fault isolation flow chart (sheet 2 of 2)