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1.故障现象 开机后透视与普通摄影工作正常,点片摄影时,曝光时间无限期延长。2.故障分析 由限时电路可知:电源变压器B_1独立绕组B_1—41,B_1—42产生的交流电压经整流、滤波稳压,作为工作电源。当押下手闸时,接触器JC_8工作,接点吸合,接通了放大管BG404电源,使BG404导通。时间继电器J_1工作并自持。松开手闸,JC_3工作,电源由R_(406)(短时间挡)或R405(长时间档),经时间电阻向C_(401)充电。当充电电压达到单结晶体管BG_(405)的发火电压时(也就是达到予置的限时时间),BG_(405)立即导通而导致
1. Symptom After the startup, the perspective and normal photography work properly. When the spot is photographed, the exposure time is extended indefinitely. 2. Fault Analysis Known by the time-limited circuit: the AC voltage generated by the power transformer B_1 independent windings B_1_41, B_1_42 is rectified, filtered, and stabilized to serve as a working power supply. When the hand brake is pressed, the contactor JC_8 works, the contact pulls in, the power of the amplification tube BG404 is turned on, and the BG404 is turned on. The time relay J_1 works and is self-sustaining. Releasing the hand brake, JC_3 works, and the power is recharged to C_(401) by R_(406) (short-term stop) or R405 (long-term stop) through time resistance. When the charging voltage reaches the firing voltage of the unijunction transistor BG_(405) (that is, the predetermined time limit is reached), BG_(405) is immediately turned on and results in