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【故障现象】HA8504型话机部分数字键不能拨号。【分析检修】该机按键号盘有四条行输入线和三条列输入线分别与拨号集成电路IC2(的①、②、③、④脚和(16)、(17)、(18)脚连接(见附图)。每按下一个数字键,触点闭合,行与列各有一条输入线的电位发生变化,这样共有4×3=12种组合方式,IC2将7个输入端输入的12种不同拨号信息进行编码,使之能按号码键的数字发出选号脉冲。当按下某一数字键时,则相应的行与列连接在一起,IC2把此输入变为相应的脉冲从输出脚输出,完成一
[Symptom] HA8504-type phone number part number keys can not dial. 【Analysis and Maintenance】 The machine keypad has four lines of input lines and three columns of input lines respectively with the dial-up integrated circuit IC2 (①, ②, ③, ④ feet and (16), (17), (18) feet connected See figure.) Each time a number key is pressed, the contacts are closed, the potentials of one input line in each row and column change, so there are 4 × 3 = 12 combinations in total. IC2 inputs 12 inputs Different dialing information is encoded so that it can issue the selection pulse according to the number key number.When a certain number key is pressed, the corresponding row and column are connected together, and IC2 turns this input into a corresponding pulse and outputs it from the output pin Complete one