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故障现象:记录笔不规则飘移,幅度不一,有时二道三道同飘,有时三道四道同飘。分析检修:根据故障现象不是所有道同时出现,故先怀疑是放大器故障,封闭前级故障消失,这证明故障发生在前级而与后级无关,但更换6N4电子管和电子管屏极电阻均未奏效。于是开始怀疑电源部分。测得前置级电源均在正常值范围内,电源纹波均小于一毫伏,但进一步观察发现+150伏电源有频率极慢的不稳定漂移,幅度约在1～2毫伏之间,而且电源的这一飘移和脑电描记笔飘移同时发生。于是对+150伏电源板进行了检查。更换了一对配对不良的差分管仍未见效。用25电烙铁对元件逐个进行加热,当加热至C_(56)
Symptoms: Pens drift irregularly and vary in magnitude. Sometimes two lanes and three lanes float together, and sometimes three lanes and four lanes float together. Analysis and maintenance: According to the phenomenon of failure, not all channels appear at the same time, so the first suspected amplifier failure, closed before the failure disappears, which proves that the failure occurred in the previous stage and has nothing to do with the latter stage, but the replacement of 6N4 electron tube and electron tube plate resistors did not work . Then began to doubt the power section. Measured pre-stage power supply is within the normal range, the power supply ripple is less than a millivolt, but further observation found that +150 volt power supply has a very slow frequency of unstable drift, amplitude of about 1 to 2 millivolts, And this drift of the power supply and the drift of the electroencephalograph pen occur at the same time. So check the +150V power board. The replacement of a pair of poorly paired differentials has still not worked. Heating the components one by one with 25 soldering irons, when heated to C_(56)