PCBA Tech - SMT patch inspection and inspection short circuit method

1. Commonly used inspection methods for SMT patches

What are the commonly used inspection and repair methods for SMT patches?

1. Visual inspection method

The common faults of smt patch can be detected based on visual effects, smell, hearing, and touch.

Visually inspect the wiring, smt patch type tin point, and electronic components for errors. After confirming that they are correct, install the battery. After powering on the radio, you can hear whether there is any abnormal sound, if there is no abnormal sound, whether there is a burning smell, and use it Touch the transistor to see if it is hot, and see if the electrolytic capacitor is cracked.

2. Resistance method

Use the MF47 digital multimeter to check whether the resistance value of the resistor chip electronic components in the circuit is correct, check whether the capacitor is broken, broken or leaking, and check whether the crystal diode and transistor are normal.

3. Voltage method

Use the DC voltage file of the MF47 digital multimeter to check the power supply and whether the static working voltage of the transistor is correct. If it is not correct, find out the reason, and check the AC voltage value at the same time.

4. Wave method

Use an oscilloscope to check the waveform of the circuit. At this time, it needs to be carried out in a state where an external data signal is input. Use an oscilloscope to check the output waveform of each transistor.

5. Current method

Use the MF47 digital multimeter DC current file to check the collector static current of the transistor to see if it meets the standard.

6. Electronic component substitution method

After the above-mentioned inspection, once it is suspected that there is a problem with an electronic component, the electronic component of the same specification and intact can be used to replace the electronic component. Once the circuit works normally after the replacement, it proves that the replaced electronic components have been damaged. This method should not be used for high-cost electronic components, because if it is not the electronic components that are damaged, unnecessary waste will occur. For high-cost electronic components, it is necessary to confirm that the electronic components are damaged before they can be replaced.

7. Step by step investigation and separation method

The step-by-step separation method can use the method of checking from the previous level to the next level, or the method of checking from the next level to the previous level. Set test method breakpoints between all levels, so that when testing methods, the scope of inspection can be narrowed, and the inspection can be carried out level by level, so that it is easier to check the location of common failure points

How to check the short circuit of SMT patch

In the manual soldering process of SMT patch, short circuit is a relatively common processing defect. To achieve the same effect as manual SMT patch and machine pasting, short circuit is a problem that must be solved. Short-circuited PCBA cannot be used. There are many ways to solve short-circuit in SMT patch processing. Let’s give you a brief introduction about SMT patch processing.

How to check the short circuit of SMT patch

1. To develop a good habit of manual welding operation, use a multimeter to check whether the key circuit is short-circuited. Every time you manually SMT an IC, you need to use a multimeter to measure whether the power supply and the ground are short-circuited.

2. Light up the short-circuited network on the PCB diagram, look for the place on the circuit board that is most likely to be short-circuited, and pay attention to the internal short-circuit of the IC.

3. If there is a short circuit in the same batch in SMT patch processing, you can take a board to cut the line, and then power on each part to check the short circuit.

4. Use a short-circuit location analyzer to check.

5. If there is a BGA chip, since all the solder joints are covered by the chip and cannot be seen, and it is a multi-layer board (above 4 layers), the power supply of each chip is divided during the design and connected with magnetic beads or 0 ohm resistors., In this way, when there is a short circuit between the power supply and the ground, the magnetic bead detection is disconnected, and it is easy to locate a certain chip.

6. Be careful when welding small-size SMT patch processing surface-mount capacitors, especially the power supply filter capacitors (103 or 104), which are large in number, which can easily cause a short circuit between the power supply and the ground.