When a circuit board is soldered, when checking whether the circuit board can work normally, it is usually not to supply power directly to the circuit board, but to follow the steps below to ensure that there is no problem in each step before powering on.
It is critical to check the schematic diagram. The first check focuses on whether the power supply of the chip and the labeling of the network nodes are correct, and also pay attention to whether the network nodes overlap. Another important point is the package of the original, the model of the package, and the pin order of the package. The package cannot use a top view, especially for non-pin packages. Check whether the wiring is correct, including wrong wiring, few wiring and multi wiring.
There are usually two ways to check the line:
1. Check the installed lines according to the circuit diagram, and check the installed lines one by one in a certain order according to the circuit connection.
2. According to the actual circuit and the schematic diagram, check the circuit with the component as the center. Check the wiring of each component pin at a time, and check whether each place exists on the circuit diagram. In order to avoid errors, the checked lines should usually be marked on the circuit diagram. It is best to use the buzzer of the ohm block of the pointer multimeter to test, and directly measure the pins of the components, so that the poor wiring can be found at the same time.
Do not power on before debugging, but 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 more serious consequences. When it comes to the power section, a 0 ohm resistor can be used as a debug method. Do not solder the resistor before power-on, check that the voltage of the power supply is normal, and then solder the resistor on the PCB to supply power to the rear unit, so as to avoid the power-on voltage of the power supply being abnormal and burning the chip of the rear unit. Add protection circuits in the circuit design, such as the use of recovery fuses and other components.
It is mainly to check the polar components, such as light-emitting diodes, electrolytic capacitors, rectifier diodes, etc., and whether the pins of the triode correspond. For triodes, the pin sequence of different manufacturers of 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, you can do more with less. The use of 0 ohm resistors is also sometimes beneficial for high-speed circuit testing. The power-on test can only be started after the above hardware test before power-on is completed.
1. Power-on observation: Do not rush to measure the electrical indicators after power-on, but observe whether there is any abnormality in the circuit, such as whether there is smoke, whether there is abnormal smell, touch the outer package of the integrated circuit, whether it is hot, etc. If an abnormal phenomenon occurs, turn off the power immediately, and then turn on the power after troubleshooting.
2. Static debugging: Static debugging generally refers to the DC test carried out under the condition that no input signal or only a fixed level signal is added. The potential of each point in the circuit can be measured with a multimeter and compared with the theoretical estimated value. Combined with the analysis of the circuit principle, determine whether the DC working state of the circuit is normal, and timely find the components in the circuit that have been damaged or are in a critical working state. By replacing components or adjusting circuit parameters, the DC working state of the circuit can meet 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, we should analyze the reasons, troubleshoot, and then debug until the requirements are met.
During the test, you cannot rely on feeling, but always observe with the aid of an instrument. When using an oscilloscope, it is best to set the signal input mode of the oscilloscope to the “DC” block. 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 the 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, make further reasonable corrections to the circuit parameters.
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