The red meter pen is grounded, the pin position in the red ring is the location, and the negative pole of the capacitor is the location. The black meter pen is placed on the IC foot to be measured, then the multimeter will display a diode value, according to the value of the diode to judge the IC. How much is the value is good, this will be based on experience, or you have a motherboard, do the right measurement on the line.

How to detect faults quickly


Look at the state of the components

Get a faulty circuit board, first observe the circuit board has no obvious component damage, such as electrolytic capacitor burn and bulge, resistance burn out and power device burn out.


Look at the welding of the circuit board

If there is no distortion warpage printed circuit board; There is no welding spot off, obvious virtual welding; The copper – clad circuit board has become warped, burnt and blackened.


A plug-in for observing components

Such as integrated circuits, diodes, circuit board power transformers and other directions are not inserted wrong.


Simply test resistance capacitance

Use a multimeter to conduct a simple test of the resistors, capacitors, inductors and other suspicious elements within the range. Test for the presence of large resistance values, capacitor short circuit, open circuit and capacitance changes, inductive short circuit and open circuit, etc.


The electrical test

After the above simple observation and test, can not remove the fault, can carry on the power test. First test the circuit board power supply is normal. Such as circuit board ac power supply is abnormal, whether the output of the regulator is abnormal, switching power output and waveform is abnormal, etc.


Brush program

For the single chip microcomputer, DSP, CPLD programmable components, you can consider brushing the program again, eliminate the circuit fault caused by the abnormal operation of the program.

How to repair circuit boards


Observation method

This method is quite intuitive, through careful examination of it, we can clearly see the burn marks. When this problem occurs, we should pay attention to the rules when conducting maintenance tests to ensure that no more serious injuries occur when the power is on. When using this method, we need to pay attention to the following problems:

Determine whether the circuit board is artificially damaged by observation. Carefully observe the components related to the circuit board, and observe each capacitor and resistor to see if there is any blackening. Since the resistance is invisible, it can only be measured with an instrument. The related bad parts should be replaced in time. Circuit board integrated circuit observation, such as CPU, AD and other related chips, observed the drum, burn and other relevant circumstances to timely modify.
The cause of the above problem may be the current side, too much current causes burning, so check the relevant circuit diagram to see where the problem is.


Static measurement

Circuit board maintenance, observation is often difficult to find some problems, unless it is obvious burning or deformation can be seen. But most of the problems still require voltmeter measurements. Circuit board components and related parts shall be inspected one by one. Repair steps should follow the following procedure.

To the power supply with the ground short circuit detection, check the cause. Check if the diode is normal. Check the capacitance for short circuit or even circuit break.
We can use observation method and static measurement method to solve most of the problems in circuit board maintenance, this is no doubt, but in the measurement to ensure that the power supply is normal, no secondary damage.


On-line measurement

On-line measurement method is often used by manufacturers. It is necessary to build a general debugging and maintenance platform for the convenience of maintenance. This method of measurement requires attention to the following steps.

Electrify the circuit board and check whether the temperature of the components is too high. If so, check out and replace the relevant components. Check the gate circuit of the circuit board, observe whether there is a problem with the logic, and judge whether the chip is good or bad. Test whether the output of crystal oscillator of digital circuit is normal.
The on-line measurement method is mainly used for the comparison of two good and bad circuit boards. Through the comparison, find the problem, solve the problem, to complete the circuit board repair.