1. - ericssonhistory.com

The same practice is adopted at the trunk exchange as at the local exchange,that traffic tests are performed in order to check the quality of service andfor fault tracing purposes. But routine tests—of tariffs, registers, lines, andthe like—are also retained to a much greater extent at the trunk exchange.The tests are at present done at fairly frequent intervals, but it has not yetbeen decided whether this will continue in future. The centralograph, whichis connected into the circuit every time a fault condition arises, is a greathelp in tracing. The intention had been to record the faults indicated by thecentralograph on punch cards, and so obtain an overall picture of the faultsand their frequency in different parts of the equipment. However, the faultshave proved too few to justify the use of this method.In traffic tests during the first six months of 1956 there were 23,080 callsto trunk exchanges. The faults numbered 480 or 2.08 %. They are classifiedin table 6, from which it is seen that the fault percentage at the trunk exchangeand local exchange is only 0.60 %.Table 6Total number of test calls 23,080Number of faults on line, repeater station ordistant exchange 342 1.48 %Number of faults at local or trunk exchange .... 138 0.60 %480 2.08 %Altogether 279 fault cards were handled during the first six months of 1956,of which 263 were cleared and 16 remained untraced. The faults are specifiedin table 7.Table 7Out-of-adjustment faults 121Dirty contacts 9Burnt contacts 2Sticking armatures 1Opens 13Shorts 34Leakage 1Soldering faults 36Installation faults 5Parts out of position 7Burnt-out coils or resistors 12Wear 9Defective components 13Other faults 0Total 263In addition, 147 faults occurred in the switchboard operators' equipmentand a few out-of-adjustment faults on keys.The time, including supervisor's time, spent on clearing faults at the trunkexchange during the period was 6,026 hours. Assuming the same conditionsduring the second six months, the time spent on maintenance per line andyear would be 9.7 hours.The number of connections established through the trunk exchange isabout 24.6 millions a year. Thus the maintenance time per 10,000 connectionsis 4.9 hours.7