How to become a hardware test engineer?

The rapid development of society is also inseparable from many hardware engineers, which is particularly important for career choices after graduation. This article will help you understand the working situation of a hardware test engineer, and at the same time, you can also know whether you can challenge such a challenge. Regarding the position of test engineer, let’s get into the topic without further ado.

Hardware detection before power on

After a circuit board is soldered, when checking whether the circuit board can work normally, you usually do not directly power the circuit board, but follow the following steps. It is not too late to power on after ensuring that there are no problems in each step.

1. Whether the connection is correct. It is critical to check the schematic diagram. The first focus of the check is whether the chip's power supply and network nodes are correctly labeled. At the same time, attention should also be paid to whether there is overlap in the network nodes. Another important point is the original package, the package model, and the pin sequence of the package; the package cannot be viewed from the top, remember! Especially for non-pin packages. Check whether the connection is correct, including wrong wires, missing wires and multiple wires.

There are usually two ways to check the wiring: 1) Check the installed wiring according to the circuit diagram, and check the installed wiring one by one according to the circuit connections in a certain order; 2) Check the actual wiring against the schematic diagram, focusing on the components. Wire. Check the connections of each component pin at a time and check whether each location exists on the circuit diagram. In order to prevent errors, the checked lines should usually be marked on the circuit diagram. It is best to use a pointer multimeter with a buzzer on the ohm block to test and directly measure the component pins, so that poor wiring can be found at the same time.

2. Is the power supply short-circuited? Do not power on before debugging. Use a multimeter to measure the input impedance of the power supply. This is a necessary step! If the power supply is short-circuited, it will cause the power supply to burn out or have more serious consequences. When it comes to the power supply section, a 0 ohm resistor can be used as a debugging method. Do not solder the resistor before powering on. Check that the voltage of the power supply is normal before welding the resistor on the PCB to supply power to the subsequent units, to avoid burning the chips of the subsequent units due to abnormal voltage of the power supply. Add protection circuits to the circuit design, such as using recovery fuses and other components.

3. Component installation status. The main thing is to check the polarized components, such as light-emitting diodes, electrolytic capacitors, rectifier diodes, etc., and whether the pins of the triodes correspond. For transistors, the pin ordering of different manufacturers with the same function is also different. It is best to test it with a multimeter.

Do open circuit and short circuit tests first to ensure that there will be no short circuit after power on. If the test points are set up well, you can get twice the result with half the effort. The use of 0 ohm resistors is also sometimes beneficial for high speed circuit testing. Only after the above hardware detection before power is completed can the power-on detection be started.

Power on detection

1. Power-on observation: After power-on, do not rush to measure the electrical indicators, but observe whether there are any abnormal phenomena in the circuit, such as whether there is smoke, whether there is any abnormal smell, whether the outer package of the integrated circuit is hot when you touch it. If any abnormality occurs, turn off the power immediately and turn on the power again after troubleshooting.

2. Static debugging: Static debugging generally refers to DC testing without adding an input signal, or only adding a fixed level signal. You can use a multimeter to measure the potential of each point in the circuit, and compare it with the theoretical estimated value. , combined with the analysis of circuit principles, determine whether the DC working status of the circuit is normal, and promptly discover components in the circuit that are damaged or in critical working status. By replacing components or adjusting circuit parameters, the DC working state of the circuit meets the design requirements.

3. Dynamic debugging: Dynamic debugging is carried out on the basis of static debugging. Appropriate signals are added to the input end of the circuit, and the output signals of each test point are sequentially detected according to the flow direction of the signals. If abnormal phenomena are found, they should be analyzed. Find out the cause, eliminate the fault, and then debug until the requirements are met.

During the test, you cannot rely on your feelings, but always observe with the help of instruments. When using an oscilloscope, it is best to set the signal input mode of the oscilloscope to "DC". Through the DC coupling method, the AC and DC components of the measured signal can be observed at the same time. Through debugging, finally check whether various indicators of the functional block and the whole machine (such as signal amplitude, waveform shape, phase relationship, gain, input impedance and output impedance, etc.) meet the design requirements. If necessary, further propose circuit parameters. Reasonable corrections.

Other tasks in electronic circuit debugging

1. Determine the test points: Develop debugging steps and measurement methods based on the working principle of the system to be adjusted, determine the test points, mark the locations on the drawings and boards, and prepare debugging data record forms, etc. 2. Set up a debugging workbench: The workbench should be equipped with the required debugging instruments. The arrangement of the instruments should be convenient for operation and observation. Special reminder: During production and debugging, be sure to keep the workbench clean and tidy.

3. Select measuring instruments: For hardware circuits, the measuring instrument should be selected for the system being adjusted, and the accuracy of the measuring instrument should be better than that of the system being tested; for software debugging, a microcomputer and development device should be equipped. 4. Debugging sequence: The debugging sequence of electronic circuits is generally carried out according to the signal flow direction. The output signal of the previously debugged circuit is used as the input signal of the subsequent stage to create conditions for the final unified adjustment.

5. Overall debugging: When selecting digital circuits implemented with programmable logic devices, the input, debugging and downloading of programmable logic device source files should be completed, and the programmable logic devices and analog circuits should be connected into a system for overall debugging and result testing.

During the debugging process, the experimental phenomena must be carefully observed and analyzed, and records must be kept to ensure the integrity and reliability of the experimental data.

Things to note during circuit debugging

Whether the debugging results are correct is largely affected by the correctness of the test quantities and test accuracy. In order to ensure the test results, it is necessary to reduce the test error and improve the test accuracy. To this end, we need to pay attention to the following points:

1. Use the ground terminal of the test instrument correctly. Use electronic instruments with a ground terminal connected to the chassis for testing. The ground terminal should be connected to the ground terminal of the amplifier. Otherwise, the interference introduced by the instrument chassis will not only change the working status of the amplifier, but also cause errors in the test results. . According to this principle, when debugging the emitter bias circuit, if you need to test Vce, you should not connect the two ends of the instrument directly to the collector and emitter. Instead, you should measure Vc and Ve to ground respectively, and then measure the two. reduce. If a dry cell-powered multimeter is used for testing, since the two input terminals of the meter are floating, they are allowed to be directly connected between the test points.

2. The input impedance of the instrument used to measure voltage must be much greater than the equivalent impedance of the measured location. If the input impedance of the test instrument is small, shunting will occur during measurement, which will bring great errors to the test results.

3. The bandwidth of the test instrument must be greater than the bandwidth of the circuit under test.

4. Choose the test point correctly. When the same test instrument is used for measurement, if the measurement points are different, the errors caused by the internal resistance of the instrument will be greatly different.

5. The measurement method must be convenient and feasible. When it is necessary to measure the current of a certain circuit, it is generally possible to measure the voltage instead of the current, because measuring the voltage does not require modifying the circuit. If you need to know the current value of a certain branch, you can get it by measuring the voltage across the resistor on the branch and converting it.

6. During the debugging process, you must not only observe and measure carefully, but also be good at recording. The recorded content includes experimental conditions, observed phenomena, measured data, waveforms and phase relationships, etc. Only by comparing a large number of reliable experimental records with theoretical results can problems in circuit design be discovered and the design plan improved.

Troubleshooting during debugging

It is necessary to carefully find the cause of the fault, and never dismantle the line and reinstall it once the fault cannot be solved. Because if it is a principle problem, even reinstalling it will not solve the problem.

1. General methods of fault inspection

For a complex system, it is not easy to accurately find faults among a large number of components and circuits. The general fault diagnosis process starts from the fault phenomenon, makes analysis and judgment through repeated testing, and gradually finds the fault.

2. Fault phenomena and causes of faults

1) Common fault phenomenon: The amplifier circuit has no input signal but an output waveform. The amplifier circuit has an input signal but no output waveform, or the waveform is abnormal. The series-connected regulated power supply has no voltage output, or the output voltage is too high and cannot be adjusted, or the output voltage stabilization performance deteriorates, and the output voltage is unstable, etc. The oscillator circuit does not produce oscillation, the counter waveform is unstable, etc.

2) Reasons for failure: If the finalized product fails after being used for a period of time, it may be due to component damage, short circuit or open circuit in the connection, or changes in conditions, etc.

3. General methods for checking faults

1) Direct observation method: Check whether the selection and use of the instrument is correct, whether the level and polarity of the power supply voltage meet the requirements; whether the pins of polar components are connected correctly, and whether there are any wrong connections, missing connections, or mutual collisions. Check whether the wiring is reasonable; whether the printed circuit board is short-circuited and whether the resistors and capacitors are burnt or exploded, etc. Turn on the power and observe whether the components are hot or smoking, whether the transformer smells burnt, whether the filament of the electron tube and oscilloscope tube is bright, whether there is high-voltage ignition, etc.

2) Use a multimeter to check the static operating point: The power supply system of the electronic circuit, the DC working status of the semiconductor transistor, integrated block (including components, device pins, power supply voltage), and the resistance value in the line can all be measured with a multimeter. When the measured value is significantly different from the normal value, the fault can be found after analysis.

By the way, it is pointed out that the static operating point can also be measured using the "DC" input mode of the oscilloscope. The advantage of using an oscilloscope is that it has high internal resistance and can simultaneously see the DC working status and the signal waveform at the measured point as well as possible interference signals and noise voltages, etc., which is more conducive to fault analysis.

3) Signal tracing method: For various more complex circuits, a signal of a certain amplitude and appropriate frequency can be connected to the input end (for example, for a multi-stage amplifier, f, 1000 HZ can be connected to the input end) sinusoidal signal), use an oscilloscope to observe the changes in waveform and amplitude step by step from the front stage to the last stage (or vice versa). If any level is abnormal, the fault is at that level.

4) Comparison method: When you suspect that there is a problem with a certain circuit, you can compare the parameters of this circuit with the same normal parameters (or theoretically analyzed current, voltage, waveform, etc.) to find out the abnormalities in the circuit. situation, and then analyze and determine the fault point.

5) Part replacement method: Sometimes the fault is hidden and cannot be seen at a glance. For example, if you have an instrument of the same model as the faulty instrument, you can replace the parts, components, plug-in boards, etc. in the instrument with those in the faulty instrument. Corresponding parts to narrow down the scope of the fault and find the source of the fault.

6) Bypass method: When there is parasitic oscillation, you can use a capacitor of appropriate capacity, select an appropriate check point, and temporarily connect the capacitor between the check point and the reference ground point. If the oscillation disappears, it means that the oscillation is generated at near this or in the front-end circuit. Otherwise, it will be at the back, and then move the checkpoint to find it. The bypass capacitor should be appropriate and should not be too large, as long as it can effectively eliminate harmful signals.

7) Short-circuit method: It is a method of temporarily short-circuiting part of the circuit to find faults. The short circuit method is most effective for detecting breaker faults. But be careful not to use the short circuit method on the power supply (circuit).

8) Circuit breaking method: The circuit breaking method is most effective for checking short circuit faults. The circuit breaking method is also a method to gradually narrow down the scope of suspected fault points. For example, if a regulated power supply is connected to a faulty circuit, causing the output current to be too large, we will disconnect certain branches of the circuit in sequence to check for faults. If the current returns to normal after disconnecting the branch, the fault occurs in this branch.

During actual debugging, there are many ways to find the cause of the fault. Only a few common methods are listed above. The use of these methods can find the fault point with one method for simple faults, but for more complex faults, multiple methods must be used to complement and cooperate with each other to find the fault point.

In general, the common practice for finding faults is:

1) Use direct observation to eliminate obvious faults.

2) Use a multimeter (or oscilloscope) to check the static operating point.

3) The signal tracing method is a simple and intuitive method that is universally applicable to various circuits and is widely used in dynamic debugging.

At the end of writing, the above are the job responsibilities of a hardware test engineer. I hope it will be helpful to engineers who want to take this position. I hope that more people will join this ranks in the future to promote the continuous innovation of equipment.