论文部分内容阅读
分析与检修:试听放音,噪声不大。不放入磁带,按下放音键,较大音量下噪声也不大。试听机内话筒录音,故障现象同上。试外接话筒录音,故障现象一样。试线路录制音乐节目,基本无噪声,录音效果尚可,只在每段节目之间的停顿处出现上述录音噪声。根据上述故障现象可以认为该机的ALC电路时间常数有问题。查阅该机的ALC(自动录音电平控制)电路,如图1所示是这部分电路。电路中,Q_1是录音通道前置放大器,Q_2是ALC控制管,D_1是半波整流二极管。这一电路的工作原理是这样:录音放大器输出的录音信号经C_(15)、R_(16)加到D_1正极,经D_1半波整流、C_(16)滤波和延时,在C_(16)上获得随录音输出信号大小而相应的ALC控制电压,这电压经R_(17)加到Q_2的基极,控制Q_2
Analysis and overhaul: audition playback, noise is not big. Do not put the tape, press the play button, the noise is not large at large volume. Listen to the machine microphone recording, the phenomenon of failure as above. Test external microphone recording, the same symptoms. Try the track recording music program, basically no noise, the recording effect is acceptable, only in the pause between the show appeared above the recording noise. According to the above symptoms can be considered ALC circuit time constant problem. Check the machine’s ALC (automatic recording level control) circuit, shown in Figure 1 is part of this circuit. In the circuit, Q_1 is the recording channel preamplifier, Q_2 is the ALC control tube, and D_1 is the half-wave rectifier diode. The working principle of this circuit is as follows: The recording signal output by the recording amplifier is added to the positive pole of D_1 via C_ (15) and R_ (16), filtered and delayed by D_1, C_ (16) Obtained with the recording output signal size corresponding to the ALC control voltage, which voltage is added to the base of Q_2 by R_ (17), control Q_2