How to detect faults quickly?
1. Look at the state of 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.
2. 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.
3. Plug-in for observing components
Such as integrated circuits, diodes, circuit board power transformers and other directions are not inserted wrong.
4. Simple test of resistance, capacitance and inductance
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.
5. Power on 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
6. Brush application
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 the circuit board?
Method one: observation
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:
The first step is to determine whether the circuit board is artificially damaged by observation. The second step is to carefully observe the components related to the circuit board. Every capacitor and resistor should be observed 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. The third step circuit board integrated circuit observation, such as CPU, AD and other related chips, the observation of 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.
Method 2: 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.
Step 1: detect the short circuit between the power supply and the ground and check the reason. Step 2: check if the diode is normal. Step 3: check whether there is a short circuit or even a circuit break in the capacitor. Step 4: check the circuit board related IC, resistance and other related device indicators.
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.
Method 3: 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.
Step 1: electrify the circuit board and check whether the temperature of the components is too high. If so, check and replace the relevant components. Step 2: 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 crystal oscillator of digital circuit is normal.
On – line measurement method is mainly used for the comparison of two good and bad circuit boards. To complete the circuit board repair.