The milliamp meter pointer of the instrument is unstable

1) The pointer of the milliamp meter is unstable. 1) Whether the light source is stable. First check whether the 220V power supply is stable? If it is unstable, you should configure a 220V stabilized power supply; then check whether the 29V DC voltage is stable? If it is unstable, it means that the filter capacitor is invalid or there is an open circuit or breakdown of a diode in the voltage rectifier bridge. It should be replaced; if the output of the sixth pin of the operational amplifier is unstable, then (1) the milliamp meter pointer is unstable 1 ) Whether the light source is stable. First check whether the 220V power supply is stable? If it is unstable, you should configure a 220V stabilized power supply; then check whether the 29V DC voltage is stable? If it is unstable, it means that the filter capacitor is invalid or a diode in the voltage rectifier bridge circuit is open or broken. It should be replaced; if the output of the sixth pin of the operational amplifier is unstable, replace the operational amplifier: if the adjustable potentiometer fails or If the contact is poor, it must be replaced.　　2) Whether there is light leakage, dampness, loose structure, etc. Shake the instrument first and observe if there is any looseness? If so, it must be tightened loosening points (to check for light leakage points). Then, cover the test path of the instrument with a black cloth, and observe whether there is any change in the milliamp meter (or observe whether there is a light leakage point in a dark room)? If there are light leaks, remove them. Next, carefully observe whether there are moisture spots on the light emitting from both sides of the dark box of the colorimeter and the photosensitive glass sheet? If the single-optical device and the photoelectric room have been heavily damp, it must be carefully cleaned, but the cleaning work must be carried out by professionals.　　3) If the light source bulb is white or black, it means that the bulb has deteriorated and must be replaced.　　4) If adjusting the '100' knob is still invalid, check whether the milliamp meter is normal and whether the pointer is stuck, and deal with it accordingly; secondly, check whether the adjustable potentiometer is normal? If the adjustable potentiometer is loose or the shaft is loose, it should be replaced; finally, check whether the operational amplifier is out of control? If the operational amplifier is out of control, it should be replaced when the bias voltage is normal.　　 (2) There is a light on but no monochromatic light. This situation is mostly caused by the loosening and displacement of the fastening screws of the light path system. The light path must be re-adjusted. (3) Zero adjustment is not possible after passing the power. Check whether the circuit system is connected to the wire or the socket is poorly connected? If yes, it must be reconnected or re-soldered; check whether RP3 and RP4 are normal? If the resistance of the resistor is changed or damaged, it should be replaced; check whether the output voltage of the amplifier is normal? If the bias voltage is normal and the voltage between pins 2 and 3 of the amplifier integrated circuit is not zero to several millivolts, check whether the output voltage of the photocell is high or low? If it is too high, the photoelectric tube is faulty or the connection wire is disconnected; if the potential of the measuring amplifier 6 pin is not the average value of the power supply, the amplifier is damaged and should be replaced.