ＨＪＤ２５６程控用户交换机故障两例张湛华１用户单机无拨号音发生这种故障时，摘机后听筒中没有拨号音，但仔细听可以感觉到有馈电，用万用表测量ａｂ线有４８Ｖ电压，其它用户拨打该用户时，听阻塞音。这种故障只发生在个别的用户（或个别的用户板上），主要原因有... HJD 256 user-controlled switchboard two cases of failure Zhang Zhanhua 1 user dial-tone machine without this failure occurs, pick up the handset after no dial tone, but carefully listen to feel fed, with a multimeter to measure ab line with 48V voltage , Other users call the user, listen to the blocking sound. This failure occurs only in individual users (or individual user board), the main reason is ...