Multimeter how to quickly detect circuit board failure

Common PCB circuit board failures are mainly focused on components, such as capacitors, resistors, inductors, diodes, transistors, field effect transistors, etc.. , as well as obvious damage to integrated chips and crystal oscillators. These faults can be found visually with the eyes, while some faults need to borrow toolshow to test pcb board with a multimeter. Today Edge Shaw will explain to you how to troubleshoot circuit boards with a multimeter:

Intuitively visible troubleshooting:

1, look at the state of the components

Find a faulty circuit board, first observe that it has no obvious component damage, such as electrolytic capacitors burned and swollen, resistors burned and power supply equipment burned.

2, look at the circuit board welding

For example, whether the printed circuit board is deformed or warped; whether there are solder joints off and obvious soldering; circuit board copper cladding board is tilted, burned black.

3, observe the plug-in components

Such as integrated system circuits, diodes, circuit boards for power supply through the transformer and other directions have not inserted the wrong.

Multimeter to detect circuit board failure.

First, the detection of ordinary diodes

Measured with a MF47 multimeter, the red and black probes were connected to both ends of the diode, readings, and then switch probes for measurement. From the results of the two measurements, low-power germanium diode forward resistance is usually 300-500ω, pcblink 1oz vs 2oz Coppersilicon diode forward resistance of about 1ω or more. The reverse resistance of germanium tubes is a few tens of kilo-ohms, and the reverse resistance of silicon tubes is over 500 kω (much smaller values for high power diodes). Good diodes have lower forward resistance and higher reverse resistance, and the greater the difference between forward and reverse resistance, the better. If the measured positive and reverse resistance are very small, close to zero, indicating that the diode internal short-circuit; if the positive and negative resistance are very large or tend to infinity, indicating that the pipe has been ruptured internally. In both cases, the diode needs to be scrapped.

Online test: test the diode PN junction positive and negative resistance, it is easier to determine whether the diode is a short-circuit breakdown or open-circuit.

Second, triode test

Turn the digital multimeter to the diode position and measure the PN junction with the probe. If the forward conduction, the number displayed is the forward voltage drop of the PN junction.

First determine the control collector and emitter; with the pen were measured students two PN junction forward voltage drop, voltage drop is emitter e, voltage drop is small collector c. In the test through the two junctions, the red pen is connected to the public pole, then the triode is tested for the NPN-type, and the red pen is connected to the base b; if the black pen is connected to the public pole, then the triode is tested for the PNP-type, and this pole is a base b. After the damage of the triode, the PN junction has two different situations: short circuit and open circuit.

On-line test: On-line test transistor, in fact, by testing the PN junction positive and negative resistance, to determine whether the transistor is damaged. When the branch resistance is greater than the positive resistance of PN junction, the normal measured positive and negative resistance should be significantly different, otherwise the PN junction will be damaged. When the branch resistance is less than the positive resistance of the PN junction, the branch should be disconnected, otherwise it is impossible to judge the quality of the transistor.

Third, the experience of MOS tube quality

1: The black stylus is connected to the D-pole, the red stylus is connected to the S-pole, there is generally 500-600 resistance

2: Under the premise of the black stylus does not move, use the red stylus to contact the G pole, and then use the red stylus to measure the S pole, there will be conduction.

3: red stylus connected to the D-pole, black stylus point below the G-pole and then connected to the S-pole The measured resistance and 1 measured is the same Description of the MOS tube work normal

Fourth, the detection of electrolytic capacitors

MF47-type multimeter for measurement, should be for the enterprise of different environmental capacity of electrolytic capacitors can choose to use the multimeter to select the appropriate range. According to the working experience, generally in this case, 47μF electrolytic capacitors provide available R × 1K file measurement, electrolytic capacitors greater than 47μF have available R × 100 file measurement.

Connect the red pen of the multimeter to the negative terminal of the capacitor and the black pen to the positive terminal. In the moment of contact, the multimeter pointer deflected significantly to the right, and then gradually to the left until it stops at a certain position (back to infinity). The resistance at this point is the forward leakage resistance of the electrolytic capacitor. The larger the value, the smaller the leakage current, the better the capacitor performance. Then, switch the red and black pens, the multimeter pointer will repeat the above swing phenomenon. However, the resistance measured at this time is the reverse leakage resistance of the electrolytic capacitor, slightly smaller than the forward leakage resistance. In other words, the reverse leakage current is greater than the forward leakage current. Practical experience shows that the leakage resistance of electrolytic capacitors should be more than a few hundred kilo-ohms, otherwise it cannot work properly.

In the test, if there is no charging phenomenon in both positive and negative phases, i.e., the meter needle does not move, it means that the capacity of the capacitor disappears or the internal circuit is short-circuited; if the measured resistance value is very small or zero, it means that the capacitor has a large leakage current or has been malfunctioned, and it can't be used again.

On-line test: The on-line test of electrolytic capacitors should only check the serious leakage or breakdown fault, while the accuracy of minor leakage or small capacity electrolytic capacitors is poor. On-line testing should also consider the effect of other components on the test, otherwise the reading will be inaccurate, affecting normal judgment. Electrolytic capacitors can also be judged by using a capacitance meter to detect the capacitance between the two ends.

detect circuit PCB Multimeter

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