First, power off check First of all, the instrument must be equipped with a certain circuit foundation and theoretical knowledge of the electronic circuit. It is necessary to understand the correct use and operation methods of the commonly used test instruments, know how to check the cause of the instrument failure, and follow the scientific work procedures on this basis. (1) Read the instruction manual of the instrument carefully, understand its working principle, and understand the circuit diagram and the accessories and Spare Parts. (2) Observe the looseness of the switch knob, dial, indicator, etc. on the instrument panel, and whether the fuse is intact. (3) Open the instrument panel cover and observe whether the internal components, power transformer connection, etc. are burnt, moldy, or falling off. At the same time of power-off inspection, not only can the internal cleaning work of the instrument be done, but more importantly, various obvious fault locations can be found, so that the fault can be judged and eliminated more quickly. For example, when the tube is leaking, there is a milky white substance inside the tube. When the electrolytic capacitor breaks down, most of it flows out of the electrolyte or the outer casing bursts. When the resistance is damaged, it will turn black or burnt. When the diode, transistor, and voltage regulator are broken down, the outer casing will also become black, burnt, and burst. There is a burnt smell and trace when the transformer burns out. Therefore, power failure inspection is an important step in the maintenance of instrumentation. However, it should be pointed out that special care should be taken during maintenance. It is not a matter of simply replacing the damaged device. Instead, the circuit diagram of the instrument should be further checked to truly understand the location and cause of the damaged device in order to analyze the real cause of the damage. For example, in the maintenance of the SP2305 gas chromatograph, when the carrier gas is not turned on before the startup (violation of the operating procedures), the tungsten of the thermal conductivity cell is blown, and there is no bridge current. If you check carefully, you will find the thermal conductivity tungsten wire. Broken, using this method, the power failure will only use the multimeter to measure the fault location, which is often encountered in our maintenance. During the maintenance process, some found that the components in the circuit are desoldered and the contact is bad, which will affect the normal operation of the circuit. Therefore, the power-off inspection method is relatively intuitive and effective. Second, power transmission check If the problem is not found in the power failure check, the "power transmission" should be used for inspection to further find the specific part of the instrument failure in order to replace the component that caused the failure. In order to avoid the expansion of the instrument fault and facilitate repeated observation, a stepwise pressurized power supply method can be used. When checking the power transmission, be sure to pay attention to the indicator light? Whether the fuse, transformer, and rectifier work normally. If an abnormality is found, immediately turn off the power and adjust the voltage of the regulator back to 0V. If you can't see the damaged component, you can turn it on again and gradually increase the observation. The purpose of this is to prepare for the following power transmission check. If there are no abnormalities at this time, the parts of the instrument can be electrically measured. The measurement order is generally: rectified input voltage - regulated output voltage - the operating current, voltage and static operating point voltage of each level, from which part of the fault is found, the method is as follows. 2.1 Measuring voltage method According to the schematic diagram of the instrument, measure the corresponding voltage value of its voltage points. If the measured voltage is very different from the one listed in the instruction manual, it is the fault. If the measured voltage is not much different from the instruction manual, the static operation of the circuit is normal. This method is effective in tubes, transistors or integrated circuits. 2.2 Simple interference method This method is especially suitable for the recorder and digital processor of the analytical instrument. When a small screwdriver is used to bump the signal input end, observe whether the pointer moves. With this method, it can be carried out step by step in the case of power transmission, and the collision is gradually made forward from the latter stage, and which level is not reflected, indicating which level the fault is at. 2.3 Injection Signal Method Use an external external signal source as the detection signal and use the terminal indicator of the unit to indicate the result of the test. That is, the external corresponding signal source is used to inject from the input end of the instrument terminal indicator to be repaired, and then the pre-stage circuit is sequentially shifted, and the test signal is injected into the input end of each stage circuit, and the instrument terminal indicator is observed or not. As a part to determine the existence of the fault and to analyze the cause of the fault. According to which level the signal is injected, if the terminal indicator does not respond, the fault is at which level. This is also a relatively simple and effective method. 2.4 Oscilloscope method This is mainly used in dynamic measurement, that is, dynamic measurement should be used when the static measurement of the instrument being repaired is normal and the fault location is not found. Using the oscilloscope to perform step-by-step observations against the schematic, and analyzing the waveforms at the relevant locations, you can also find the exact location of the fault. This method is often used in the electronic amplification section of the maintenance automation instrument, which is very successful. However, this method requires maintenance personnel to be familiar with the circuit principle and waveform changes of the instrument being repaired, and requires skilled operation and proper use of the oscilloscope to observe signals of various variations. 2.5 Device Replacement Method When it is not possible to determine the approximate range of instrument failure, a unit replacement or a single board replacement method may be employed. Be careful not to disassemble the components in the circuit, especially the precision instruments, and do not allow them to be disassembled. It is possible to use devices of the same model, the same specifications, and the same structure. The unit is plugged in to temporarily replace the questionable part and observe its effect on the fault. If the fault disappears, it indicates that the replaced part is faulty. This method is particularly suitable for tube circuits or printed circuit board circuits, integrated circuits. 2.6 step-by-step breaking method Some instruments have complex circuit components, involve many components, and affect each other or in many ways. Some instrument failures manifest as one level, while the real part of the failure is at the next level. For example, in the counting circuit, since the input impedance of the next stage acts too much on the load of the upper stage, the counting is stopped. When overhauling this type of instrument, it is possible to separate the stages from the back to the front until the fault is found. When using this method, be sure to select the location of the break point. Only when it is properly disconnected can the fault location be determined quickly. At the same time, it is necessary to prevent the voltage from being too high or too low in other parts due to the disengagement of a certain part. Third, troubleshooting When the faulty part of the instrument being instrumented and the cause of the fault are detected, the fault can be dealt with after the power is turned off. Be sure to pay attention during the process: (1) The power must be cut off, and the power should be shut down for processing; (2) When the component needs to be replaced, it should be the same as the original component and the qualified component of the same specification. If it is not possible, it can be replaced by components that are similar to the same machine. Try not to change the original circuit structure so as not to affect the electrical performance of the instrument; (3) When soldering field effect transistors or integrated circuits, take care to prevent leakage and static electricity from damaging the components. Therefore, it is required to have a good grounding of the soldering iron, otherwise it should be disconnected and welded; (4) When the power transformer is damaged and needs to be re-wound, it is necessary to clarify the data of each winding of the original transformer and try to keep the original parameters. Jinling Instrument Mini concrete mixer can be used to mix dry hard concrete, plastic concrete, flow concrete, light aggregate concrete and various mortars, so they were popular in precast concrete plants, industrial and civil construction works, bridges, water works, roads, airport and harbors. JS series mini Concrete Mixers are double horizontal axle forced mixers with two advantages of independent performance or forming simple concrete mixing plants with PLD series of batching machines. 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