Several methods of instrumentation fault diagnosis

Instrument and instrument circuit maintenance has always been an indispensable part in electronics companies. Because only through it can make the original unqualified product finally leave the factory. However, maintenance is also the most complicated part of electronics companies. Because it not only uses many electronic expertise, it also sometimes requires extensive field experience.

1, knocking hand pressure method

When we use the instrument, we often encounter the phenomenon of good or bad operation of the instrument. The vast majority of this phenomenon is caused by poor contact or welding. For this situation, tapping and hand pressure can be used.

The so-called "knocking" is to tap the board or component with a small rubber mallet or other knocker on the part that may be faulty to see if it will cause an error or stop failure. The so-called "hand pressure" is when the fault occurs, after the power is turned off, the plugged parts and the plug and the base are pressed again by hand, and if the power supply is turned on, it will eliminate the fault. If it is found that knocking the case is normal and the beat is not normal, it is better to re-insert all the joints and try again. If it is not successful, you have to think of other methods.

2, observation method

Uses sight, smell, touch. In some cases, the damaged components will discolor, blistering, or burn spots; burned devices will produce some special odors; short-circuited chips will become hot; visible or unwelded areas can also be observed with the naked eye. .

3, elimination method

The so-called exclusion method is to determine the cause of the fault by inserting and removing some plug-in boards and devices. When the instrument returns to normal after removing a certain board or device, it indicates that the failure occurred.

4, replacement method

Two instruments of the same type or enough spare parts are required. Replace a good spare with the same component on the faulty machine and see if the fault is eliminated.

5. Comparison method

Two instruments of the same type are required and one is in normal operation. Use this method also has the necessary equipment, for example, multimeter, oscilloscope and so on. According to the nature of comparison, there are voltage comparison, waveform comparison, static impedance comparison, output comparison, and current comparison.

The specific method is: let the faulty meter and the normal meter operate under the same conditions, and then detect the signals of some points and then compare the measured two signals. If they are different, you can conclude that the fault is out here. This method requires maintenance personnel with considerable knowledge and skills.

6, lift the temperature method

Sometimes, the instrument work for a long time, or in the summer when the working environment temperature is high, it will malfunction, shut down and check normally, stop for a period of time and then boot again and normal, after a while there will be a failure. This phenomenon is due to the poor performance of individual ICs or components, and the high temperature characteristic parameters do not meet the specification requirements. In order to find out the cause of the malfunction, it is possible to use the heating and cooling method.

The so-called cooling, that is, in the event of a failure, the use of cotton fiber will be wiped in the area of ​​possible failure of the alcohol to make it cool, observe whether the failure is eliminated. The so-called warming is artificially raising the temperature of the environment, such as using a soldering iron near the point of doubt (note that the temperature must not rise too high to damage the normal device) to see if the fault appears.

7, riding method

The riding method is also called parallel method. Place a good IC chip on the chip to be inspected, or connect good components (resistance capacitors, diodes, transistors, etc.) in parallel with the components to be inspected to maintain good contact if the fault is caused by an open circuit inside the device or For poor contact and other reasons, this method can be ruled out.

8, capacitor bypass method

When a circuit produces a strange phenomenon, such as a disorganized display, the capacitor bypass method can be used to determine the portion of the circuit that has failed. Connect the capacitor across the power supply and ground of the IC. Connect the transistor circuit across the base input or collector output. Observe the effect on the fault. If the fault phenomenon disappears when the capacitor bypass input is inactive and its output is bypassed, a fault is identified in this stage of the circuit.

9, state adjustment method

In general, do not touch the components in the circuit before the fault is determined. This is especially true for adjustable devices such as potentiometers. However, if multiple reference measures are taken in advance (for example, position marks or voltage values ​​or resistance values ​​are measured before being touched), they are allowed to act if necessary. Maybe after some change, the fault will be eliminated.

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 enveloping gradually narrow down the fault search range, together with signal comparison, component exchange and other methods, generally the fault will be found quickly.

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