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一部HA238(Ⅲ)P/TSD的免提电话机,不慎误接入市电,造成接线盒烧焦并无法拨打(发号)故障(包括免提功能),发光二极管不亮,同时,耳机中也听不到侧音;但来话时铃声正常。 检修:打开机壳,发现限流电阻R_0(阻值为18Ω)已烧黑,由此判断极性保护电路(过压保护二极管或压敏电阻)被击穿。先用万用表测量过压保护二极管CZ_1,正反向电阻均为0Ω,焊下测量还是如此,证明已经击穿;将R_0电阻焊下,用另一阻值为18Ω的电阻换上,此时,接上外线试听有拨号音,再试拨,发号正常,声音也清晰,说明手柄通话电路无故障;再试用免提键,对方能听到我方
A HA238 (Ⅲ) P / TSD speakerphone accidentally misconnected to the mains, resulting in the junction box burned and unable to dial (issue) fault (including hands-free function), the light-emitting diode does not shine at the same time, The earphones also do not hear the sidetone; but the ringtone is normal. Overhaul: Open the case and found the current limiting resistor R_0 (resistance 18Ω) has been burned black, which determines the polarity protection circuit (overvoltage protection diode or varistor) is breakdown. First with a multimeter to measure the over-voltage protection diode CZ_1, the forward and reverse resistance are 0Ω, measured under the welding or so, that has been breakdown; the R_0 resistance welding down, with another resistance 18Ω resistance replaced, at this time, Listen to a dial tone outside the trial, try dialing, normal number, the sound is also clear, indicating that the phone handle the fault-free; try the hands-free keys, the other party can hear our side