1. Percussion hand pressure method Often encounter the phenomenon of ups and downs when the instrument is running, most of this phenomenon is caused by poor contact or virtual welding. For this situation, percussion and hand pressure can be used. The so-called percussion is to tap the plug-in board or component with a small rubber buckle or other percussion objects to see if it will cause an error or shutdown failure on the part that may cause failure. The phenomenon of good and bad when the instrument is running, most of this phenomenon is caused by poor contact or weak welding. For this situation, percussion and hand pressure can be used. The so-called 'knock' is to tap the plug-in board or component lightly with a small rubber flap or other knocking objects to see if it will cause an error or shutdown failure on the part that may cause failure. The so-called 'hand pressing' means that when a fault occurs, the components, plugs and sockets that are inserted after the power is turned off are pressed firmly by hand, and then the power is turned on to try whether the fault will be eliminated. If you find that it is normal to tap the case, and then it is not normal, it is best to re-plug all the connectors firmly and try again. If it is unsuccessful, you have to find another way. 2. Observation method uses vision, smell and touch. Sometimes, damaged components will change color, blistering or burnt spots; burnt components will produce some special smell; short-circuited chips will be hot; we can also observe the virtual soldering or desoldering with the naked eye . 3. Elimination method The so-called elimination method is a method of judging the cause of the fault by plugging in some plug-in boards and components in the machine. When a plug-in board or device is removed and the instrument returns to normal, it means that the fault has occurred there. 4. The replacement method requires two instruments of the same model or sufficient spare parts. Replace a good spare part with the same component on the faulty machine to see if the fault is eliminated. 5. The comparison method requires two instruments of the same model, and one of them is operating normally. To use this method, you must have the necessary equipment, such as a multimeter, an oscilloscope, and so on. According to the nature of comparison, there are voltage comparison, waveform comparison, static impedance comparison, output result comparison, current comparison, etc. The specific method is: let the faulty instrument and the normal instrument run under the same conditions, and then detect the signals at some points and compare the two sets of signals measured. If there are differences, you can conclude that the fault is here. This method requires maintenance personnel to have considerable knowledge and skills. 6. Temperature rise and fall method Sometimes, the instrument will work for a long time, or when the working environment temperature is high in summer, it will malfunction. Turn off and check it is normal, stop for a period of time and turn it on again and then it will be normal. This phenomenon is due to the poor performance of individual ICs or components, and the high temperature characteristic parameters fail to meet the index requirements. In order to find out the cause of the failure, the heating and cooling method can be used. The so-called cooling means that when a fault occurs, wipe anhydrous alcohol with cotton fiber on the part that may be faulty to cool it down and observe whether the fault is eliminated. The so-called warming is to artificially raise the ambient temperature, such as using an electric soldering iron to put it close to the suspected part (note that the temperature must not be raised too high to damage the normal components) and try to see if the fault occurs. 7. Shoulder riding method Shoulder riding method is also called parallel method. Put a good IC chip on the chip to be inspected, or connect a good component (resistance capacitor, diode, triode, etc.) in parallel with the component to be inspected, and keep good contact. If the fault is caused by an open circuit or Reasons such as poor contact can be ruled out by this method. 8. Capacitor bypass method When a certain circuit produces a strange phenomenon, such as a display disorder, the capacitor bypass method can be used to determine the part of the circuit that is probably malfunctioning. Connect the capacitor across the power and ground terminals of the IC; connect the transistor circuit across the base input or collector output, and observe the effect on the failure phenomenon. If the input terminal of the capacitor bypass is invalid and the fault disappears when the output terminal is bypassed, it is determined that the fault has occurred in this stage of the circuit. 9. State adjustment method Generally speaking, before the fault is determined, do not touch the components in the circuit casually, especially the adjustable devices, such as potentiometers. However, if you take pre-reference measures (for example, make a position mark or measure the voltage or resistance value before touching it), you can still allow touching if necessary. Maybe the fault will be eliminated sometimes after the change. 10. Isolation method fault isolation method does not require the same type of equipment or spare parts for comparison, and it is safe and reliable. According to the fault detection flow chart, segmentation and encirclement gradually narrow the fault search range, and with signal comparison, component exchange and other methods, the fault will generally be found quickly
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