Instrumentation troubleshooting tips

In the process of using the instrument, certain faults will occur. After a fault occurs, the fault should be diagnosed in a timely manner to find out the cause quickly and then put the instrument into use to reduce the loss. When diagnosing a fault, it requires a certain amount of experience and skill. If the method of diagnosing a fault is correct, you can quickly check out where exactly the problem has arisen and solve the problem effectively.

1, knocking hand pressure method often encounters 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 lightly hit the board or component with a small rubber hoe or other knocker 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 when the cabinet is normal and the beat is not normal, it is better to re-insert all the joints and try again. If you are unsuccessful, you have to find another solution.

2. The observation method uses vision, smell, and 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. Exclusion method The so-called exclusion method is a method of determining the cause of failure 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. The replacement method requires two instruments of the same type or sufficient spare parts. Replace a good spare with the same component on the faulty machine and see if the fault is eliminated.

5. The comparison method requires two instruments of the same type, 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, temperature rise and fall method Sometimes, the instrument work for a long time, or in the summer when the working environment temperature is high, there will be failure, shutdown check is normal, stop for a period of time and then boot and normal, after a while there is 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 requirements of the specification. 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 place 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 shoulder law riding shoulder method is also called parallel law. 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 reasons such as poor contact, this method can be ruled out.

8. Capacitance bypass method When a circuit produces a strange phenomenon, such as a display chaos, you can use the capacitor bypass method to determine the part 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, before the failure is not determined, do not touch the circuit components, especially adjustable devices, such as potentiometers. However, if multiple reference measures are taken beforehand (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 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, the fault will generally be quickly found.