Circuit board debugging

Circuit board debugging

The commonly used instruments for debugging are ： regulated power supply 、 A multimeter 、 Oscilloscope 、 Spectrum analyzer and signal generator etc .
The significance of debugging is ： Through debugging, the electronic circuit can reach the specified index ; Through debugging, defects in the design are found and corrected .

General steps of circuit debugging ：
A simple system
Power debugging -> Board debugging -> Joint tune
Complex system
Power debugging -> Board debugging -> Extension debugging -> Host debugging -> Joint tune

Specific steps
（1） Electrify and observe ： Do not rush to measure electrical indicators after power on , Observe whether the circuit is abnormal , For example, whether there is smoke , Is there any abnormal smell , Touch the IC package by hand , Is it hot or not . If there is any abnormality , Turn off the power supply immediately , Power on after troubleshooting .
（2） Static debugging ： Static debugging generally refers to no input signal , Or DC test with only fixed level signal , The potential of each point in the circuit can be measured with a multimeter , By comparing it with the theoretical estimate , Combined with the analysis of circuit principle , Judge whether the DC working state of the circuit is normal , Find out the damaged or critical components in the circuit in time . By changing devices or adjusting circuit parameters , Make the DC working state of the circuit meet the design requirements .
（3） Dynamic debugging ： Dynamic debugging is based on static debugging , Add the appropriate signal to the input of the circuit , According to the direction of the signal , The output signals of each test point are detected in sequence , If abnormal phenomena are found , The reason should be analyzed , And get rid of the trouble , Then debug , Until the requirements are met .

When using an oscilloscope , It is better to set the signal input mode of the oscilloscope to “DC” block , Through DC coupling , The intersection of measured signals can be observed at the same time 、 DC components .

Some problems in circuit debugging
（1） According to the working principle of the system to be debugged （ Schematic and PCB） Develop commissioning steps and measurement methods , Determine the test point , And mark the position on the drawing and board , Draw the debugging data record form, etc .
（2） Set up the debugging workbench , The worktable is equipped with the required debugging instruments , The equipment should be easy to operate , Convenient for observation .
（3） For hardware circuits , Measurement instruments shall be selected for the system being commissioned , The accuracy of the measuring instrument shall be better than that of the tested system ; For software debugging , It should be equipped with microcomputer and development tools .
（4） The debugging sequence of electronic circuits is generally carried out according to the signal flow direction , Take the output signal of the previously debugged circuit as the input signal of the later stage , To create conditions for the final unification .
（5） Choose the digital circuit realized by PLC , The input of PLD source file shall be completed 、 Debugging and downloading , And the programmable logic devices and analog circuits are connected into a system , Conduct overall debugging and result test .
（6） In the course of debugging , We should carefully observe and analyze the experimental phenomena , Keep a record , Ensure the integrity and reliability of experimental data .

There are usually two ways to check the line ：
1） Check the installed wiring according to the circuit diagram ： This method is characterized by , Connect wires according to the circuit diagram , Check the installed lines one by one in a certain order , From this, it is easy to check the error line and less line .
2） Check the line according to the actual line and the principle circuit ： This is a way to look up lines with components as the center . Put each element （ Including devices ） Check the connection of pin once , Check if there is... On the circuit diagram , This method can not only find out the wrong line and less line , It's easy to detect multiple lines .

Installation of components
Check whether there is short circuit between the pins of components ; Whether there is poor contact at the connection ; diode 、 triode 、 Whether the integrated device and the polarity of electrolytic capacitor are connected correctly .

Power supply （ Including polarity ）、 Is the signal source connected correctly .

Whether there is a short circuit between the power end and the ground .

Debugging method
Debugging includes testing and adjusting .

So called electronic circuit debugging , It is a series of measurements for the purpose of achieving the circuit design index → Judge → adjustment → The repeated process of remeasurement . In order to make the debugging run smoothly , It is better to indicate the potential value of each point on the designed circuit diagram , Corresponding oscillogram and other main data . The debugging method is usually divided into debugging first and then joint debugging （ The main tune ）.

Debugging can follow the flow direction of the signal , Adjust each unit circuit step by step , Make its parameters basically conform to the design index . The core of this debugging method is ： The functional blocks that make up the circuit （ Or basic unit circuits ） First of all, debug , And on this basis, gradually expand the scope of debugging , Finally, complete the whole machine debugging . Use the first tone , The advantage of post joint debugging is ： Be able to find and solve problems in time . This method is generally used in newly designed circuits .

For including analog circuits 、 The electronic devices of digital circuit and microcomputer system should be debugged in this way . Because only after debugging the three parts separately , Respectively reach the design target , And through the signal and level conversion circuit to achieve the whole machine joint debugging . otherwise , Due to the input required by each circuit 、 Output voltage and waveform do not match , Blind joint debugging , It may cause a lot of damage to the devices .

Precautions during commissioning
（1） Use the grounding terminal of the measuring instrument correctly
（2） The input impedance of the instrument used to measure the voltage must be much greater than the equivalent impedance of the measured place. If the input impedance of the measuring instrument is small , It will cause shunt during measurement , Bring great error to the measurement result .
（3） The bandwidth of the measuring instrument must be greater than the bandwidth of the circuit under test
（4） Choose the right measuring point
（5） The measurement method should be convenient and feasible
（6） During commissioning , Not only should we observe and measure carefully , And be good at recording

Troubleshooting when debugging
（1） A general way to check for faults
General troubleshooting process , Starting from the failure phenomenon , Pass the repeated test , Make analytical judgments , The process of finding out the cause of a fault step by step .
1） Direct observation ： Direct observation means not using any instrument , Take advantage of people's sight 、 listen 、 Smell 、 Touch, etc. as a means to find problems , Find and analyze faults . Direct observation includes power off inspection and power on observation .
2） Check the static working point with a multimeter
3） Signal tracking
4） Contrast
5） Component replacement method
6） Bypass method
7） Short circuit method
8） Open circuit method

（2） Failure phenomena and causes of failure
The cause of the failure may be the damage of components , There is a short or open circuit in the wiring （ If the solder joint is faulty 、 The connector is in poor contact 、 Variable resistor 、 Potentiometer 、 Poor contact of semi variable resistance 、 The surface of contact surface is oxidized, etc ）, Or the use conditions change （ Such as grid voltage fluctuation , A working environment that is too cold or too hot ） Affect the normal operation of electronic equipment .

For newly designed and installed circuits , The cause of the problem may be ： The actual circuit is not in accordance with the designed schematic diagram ; Component welding error 、 Improper use or damage of components ; There are some serious shortcomings in the circuit itself , Does not meet the technical requirements ; There is a short circuit or open circuit in the wiring .

Malfunction caused by improper use of the instrument , If the oscilloscope is not used correctly, the waveform is abnormal or there is no waveform , If the grounding problem is handled improperly, interference will be introduced .