1172 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956 



multiple split into groups of ten. The 40 verticals of the latter are con- 

 nected directly to the 40 test set feature circuits designated 0-39. 



Two additional 10 X 20 crossbar switches perform the function of 

 connecting any of the five power or five multiple terminations to any 

 of the forty test set features. These terminations are comprised of 5 

 loops and one each of ground, negative 24 volts, negative 48 volts, 90- 

 volt 20-cycle ringing current and positive 130 volts. 



Thus it can be seen that, through proper operation of the primary, 

 secondary, tertiary and terminating crossbar switch cross points, a 

 path can be established from any circuit terminal to any test set feature 

 and supplied with any of the available power or loop terminations. It is 



7 CROSSBAR 

 SWITCHES 



RELAY 



SWITCHING 



TYPE CIRCUIT 



UNDER TEST 



MAX. 99 

 LEADS 



AUTOMATIC 

 SWITCHING 



OF CIRCUIT 



TERMINALS TO 



DESIRED TEST 



FEATURES 



QUICK CONNECT 



CONTACT FIXTURES 



TELETYPE TRANSMITTER 



MODIFIED FOR 5-WIRE 



OPERATION 



40 



LEADS 



CONNECT «. 



DISCONNECT 



SIGNALS 



TRANSMITTED 



CODES 



5 LEADS 



TEST 

 FEATURES 



CIRCUITS APPLY 



DIFFERENT TESTS 



AND CHECKING 



CONDITIONS 



40 

 LEADS 



TEST 



FEATURE 



SIGNALS 



TAPE 

 DECODING 

 CIRCUITS 



10 KEYS 



OPTIONAL 

 FEATURES 

 CIRCUITS 



PERMITS VARIATION 



OF TEST LISTED ON 



STANDARD TAPES 



TEST SIGNALS AND CHECK RESPONSE 



2 CROSSBAR 

 SWITCHES 



CONTROL 

 CIRCUITS 



A SPECIAL CODE AT 

 END OF EACH TEST 

 STEP PERMITS THESE 

 CIRCUITS TO TRANS- 

 FER CONTROL OF THE 

 TRANSMITTER TO THE 

 CHAIN LEAD 



RESET KEY 



INDEXES TAPE i^ 

 TO STARTING 

 POSITION i 



TERMINATION 

 SWITCHING 

 OF POWER 

 8. SIGNALS 

 t130VDC GROUND 

 90V PO'^ RING 5 LOOPS 

 -48 V DC -24 V DC 



TO TEST 

 FEATURES CIRCUITS 



TERMINATION 



SWITCHING 



SIGNALS 



TROUBLE 



INDICATING 



CIRCUITS 



1. LAMPS INDICATE 

 PROGRESS OF TEST 

 AND ANY FAILURES 



2. INDICATES FAILING 

 CIRCUITS 



3. SHOWS POSITION OF 

 RELAYS IN TESTED 

 CIRCUITS 



(-—CHAIN LEAD 



CHECKS POSITION OF ALL TEST 

 FEATURE RELAYS WITH WATCH- 

 ING RELAYS. IF CHAIN IS 

 CLOSED, TAPE IS INDEXED TO 

 NEXT TEST CODE POSITION. 

 IF CHAIN IS OPEN, CONTROL 

 CIRCUIT WILL SWITCH TO 

 TROUBLE INDICATING CIRCUITS 



START KEY 



STARTS AUTOMATIC 



PROGRESSION 



OF TAPE 



Fig. 13 — Block schematic. 



