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BELL SYSTEM TECHNICAL JOURNAL 



Trouble indicator circuits are provided for use in connection with 

 the test and maintenance of the marker circuits. These circuits are 

 arranged so that when trouble is encountered by a marker, the marker 

 will seize the trouble indicator and operate combinations of relays and 

 light small lamps which indicate the nature and the location of the 

 failure and give an alarm to the maintenance force. 



Equipment 



Figure 16 shows a typical switch frame used in the crossbar system. 

 This particular frame is a "line link" frame which serves a group of 

 subscribers for both originating and terminating traffic. The frame- 

 works on which the equipment is mounted are constructed of rolled 



Fig. 16 — Line link frame. 



