How to troubleshoot a circuit board with a multimeter

The red test lead is grounded, the pins in the red circle are all locations, and the negative poles of the capacitors are all locations. Put the black test lead on the IC pin to be measured, and then the multimeter will display a diode value, and judge the quality of the IC based on the diode value. What is a good value? It depends on the experience. Either you have a motherboard and do comparison measurements.
How to troubleshoot a circuit board with a multimeter
How to quickly detect a fault on a circuit board
1, look at the status of the component
Get a faulty circuit board, first observe whether the circuit board has obvious component damage, such as electrolytic capacitor burnout and swelling, resistor burnout, and power device burnout.
2, look at the soldering of the circuit board
Such as whether the printed circuit board is deformed or warped; whether the solder joints fall off or obvious weak soldering; whether the copper clad skin of the circuit board is warped, burned and turned black.
3, the plug-in of the observation component
The direction of the integrated circuit, diode, circuit board power transformer, etc. is correct.
4, simple test of resistance, capacitance and inductance
Use a multimeter to perform simple tests on suspected components such as resistance, capacitance, inductance, etc., to test whether the resistance value increases, capacitor short circuit, open circuit and capacitance change, inductance short circuit and open circuit.
5. Power-on test
After the above simple observation and test, the fault cannot be eliminated, and the power-on test can be carried out. First test whether the power supply of the circuit board is normal. Such as whether the AC power supply of the circuit board is abnormal, whether the output of the voltage stabilizer is abnormal, whether the output of the switching power supply and the waveform are abnormal, etc.
6, brush the program
For programmable components such as single-chip microcomputer, DSP, CPLD, etc., you can consider re-flashing the program to eliminate the circuit failure caused by abnormal program operation.
How to repair the circuit board
Method 1: Observation method of circuit board repair
This method is quite intuitive. Through careful inspection, we can clearly see the burnt traces. When this problem occurs, we must pay attention to the rules during maintenance and inspection to ensure that no more serious injuries occur when the power is turned on. When we use this method, we need to pay attention to the following issues:
Step by observation to determine whether the circuit board is artificially damaged. The second step is to carefully observe the related components of the circuit board, and observe every capacitor and resistance to see if there is any blackening. Since the resistance cannot be seen, it can only be measured with an instrument. Related bad parts should be replaced in time. The third step is to observe the circuit board integrated circuit, such as CPU, AD and other related chips. If you observe bulging, burning and other related conditions, you should modify it in time.
The cause of the above problems may be in the current. Excessive current can cause burnout, so check the relevant circuit diagram to see where the problem is.
Method 2: Static measurement method of circuit board repair
In circuit board repair, it is often difficult to find some problems by observation method, unless it is obvious that it is burned or deformed. But most of the problems still need to be measured by a voltmeter before a conclusion can be drawn. Circuit board components and related parts should be tested one by one. The repair procedure should be operated according to the following procedure.
Step: Detect the short circuit between the power supply and the ground, and check the reason. Step 2: Check if the diode is normal. The third step: Check whether the capacitor has a short circuit or even an open circuit. The fourth step: check the circuit board-related integrated circuits, as well as resistance and other related device indicators.
We can solve most of the problems in circuit board maintenance by using observation method and static measurement method. This is unquestionable, but during the measurement, ensure that the power supply is normal and no secondary damage can occur.
Method 3: On-line measurement method for circuit board repair
On-line measurement method is often used by manufacturers. In order to facilitate maintenance, it is necessary to build a general debugging and maintenance platform. When measuring in this way, you need to pay attention to the following steps.
Step: Power on the circuit board, check whether the component is overheated, if so, check it out and replace the relevant component. The second step: Check the gate circuit corresponding to the circuit board, observe whether there is a problem with the logic, and determine whether the chip is good or bad. Step 3: Test whether the output of the crystal oscillator of the digital circuit is normal.
On-line measurement method is mainly used to compare two good and bad circuit boards. Through the comparison, problems are found and solved. So as to complete the repair of the circuit board.