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故障现象:按定标键,八支描笔均无定标出现且缓慢乱摆,但时标正常。分析检修:按常规,首先检查电源。打开机器左侧面板,用500型万用表先测±12V电压,正常无误。查±20V电压,测得其输出电压只有8V左右。拔出该板仔细检查,发现桥式整流二极管BG401～BG404(2CP3A×4)中的两只开路损坏,更换后20V输出电压正常。再开机,发现定标功能恢复,但描笔仍旧缓慢乱摆。继续检查+150V及-10V电源,发现+150V电压高达210V以上。+150V稳压电源原理图中,BG 53为调整管,BG55～BG58为两级差分放大器,BG57的基极接参考电压,该电压由D76、D77产生,BG58连接取样电压。假定某种原因使输出电压上升,
Symptoms: According to the calibration key, the eight pens have no calibration and are slowly swinging, but the time scale is normal. Analytical maintenance: As usual, first check the power supply. Open the left side panel of the machine and measure the ±12V voltage with a 500-type multimeter, which is normal and correct. Check ± 20V voltage, measured its output voltage is only about 8V. Pull out the board and inspect it carefully and find that two of the bridge rectifier diodes BG401-BG404 (2CP3A×4) are open-circuited and the output voltage of 20V is normal after the replacement. After booting, it was found that the calibration function was restored, but the pen was still slowly swinging. Continue to check the +150V and -10V power supplies and find that the +150V voltage is as high as 210V or more. +150V regulated power supply schematic diagram, BG 53 for the adjustment tube, BG55 ~ BG58 two differential amplifier, BG57 base connected to the reference voltage, the voltage generated by the D76, D77, BG58 connected sampling voltage. Assuming some reason to increase the output voltage,