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故障现象:接通电源开关后,电表指针立刻向右偏转到100％处,无法返回“0”位(光电管暗合前光门未打开)。更换光电管暗合内硅胶或用热风干燥均无效。分析与检修:721型分光光度机的有关电路如附图所示,它采用5G23B运算放大器作为灵敏变换级。该运算放大器有两个输入端,“2”端接光电微电流放大器,“3”端接调零电路,二个输入端不平衡就会导致指针偏转,因此故障就可能是这两部分电路工作不正常引起的。经检查:调零(细调)电位器在使用中调节过度,内部损坏,失去调节作用,使光电管的暗电流得不到补偿,放大器失调,造成灵敏电流计因有一微弱电流流过而发生偏转。更换该电位器后就能正常工作。
Symptom: Turn on the power switch, the meter pointer immediately to the right deflection to 100%, can not return to “0” bit (photocell hidden before the light door is not open). Replacing the photoelectric tube concealed silicone or hot air drying are invalid. Analysis and Maintenance: 721 spectrophotometer related circuit shown in the figure, which uses 5G23B operational amplifier as a sensitive conversion level. The op amp has two inputs, “2” terminates the opto-electronic micro-current amplifier, “3” terminates the zeroing circuit, unbalanced two inputs cause the hands to deflect, so the fault may be the work of both circuits Not normally caused. After checking: Zero adjustment (fine adjustment) Potentiometer in use over-regulation, internal damage, loss of regulation, so that the photocurrent dark current can not be compensated, the amplifier imbalance, resulting in a sensitive galvanometer flows through a weak current occurred deflection. Replacement of the potentiometer will be able to work properly.