Circuit board repair tips Get it up quickly!
In the absence of any circuit schematic diagram, to repair an unfamiliar and more complicated faulty circuit board, the so-called "maintenance experience" in the past is difficult to cope with. Despite the profound technical skills of the hardware maintenance personnel of electronic technology, they are full of confidence in the maintenance work. But if you don't do it properly, you can get half the work with half the effort. So, what can we do to better improve the maintenance efficiency?
Here are a few principles to be discussed below for your reference. Make maintenance work orderly and step by step.
First, look first and then measure
The circuit board to be repaired should be visually inspected first. Observe with the help of a magnifying glass if necessary.
Mainly look at:
1. Whether there are broken wires and short-circuits; especially whether there are any cracks, adhesions, etc. on the printed board connection lines on the circuit board;
2. Whether the related components such as resistors, capacitors, inductors, diodes, transistors, etc. are disconnected?
3. Has anyone repaired it? Which components have you moved? Are there problems such as false soldering, missing soldering, and incorrect insertion?
After excluding the above conditions, at this time, first use a multimeter to measure the resistance between the power supply and the ground of the circuit board. Generally, the resistance of the circuit board should not be less than 70Ω. If the resistance is too small, it is only a few or a few ohms. It means that there are components on the circuit board that are broken down or partially broken down. Measures must be taken to find out the broken down components. The specific method is to power up the repaired board (Note! At this time, it must be clear about the voltage value and positive and negative polarity of the working voltage of the board. Do not connect wrongly and add higher than the working voltage value. Otherwise, Hurt! Old faults are not ruled out, and new ones are added! Use a thermometer to measure the temperature of each device on the circuit board. The faster and higher temperature is regarded as the key suspect.
If the resistance value is normal, then use a multimeter to measure the second and third resistors, triodes, field effect transistors, and toggle switches on the board. The purpose is to first ensure that the components being measured are normal. Do not complicate problems that can be solved with general testing tools (such as multimeters, etc.).
Second, outside first
When using for detection. If the situation allows, it is best to have a good circuit board as the reference board. Then use the tester's dual-rod VI curve scanning function to perform a good and bad comparison test on the two boards. The initial comparison test point can start from the port of the circuit board; then the comparison test is performed on the surface and inside, especially for the capacitor. This can make up for the shortcoming of the multimeter that it is difficult to detect whether the capacitor is leaking online.
Three, easy first, then difficult
When using for detection. In order to improve the test effect, before the online function test of the circuit board, some technical treatment should be performed on the board being repaired to minimize the impact of various interferences on the test process. The specific measures are as follows:
1. Preparation before test
Short the crystal (note that for the four-pin crystal, it is necessary to make sure that those two pins are signal output pins, and these two pins can be shorted. Remember that the other two pins are power pins in general. Do not short them !! Capacitor electrolytic capacitors should also be soldered to open circuit. Because the charging and discharging of large-capacity capacitors will also cause interference.
2. Test the device using the exclusion method
During the online test or comparison test of the device, any device that passed the test (or relatively normal), please directly confirm the test result and record it. If the test fails (or is relatively bad), you can test again. If it still fails, you can also confirm the test results. This continues until the device on the board is tested (or compared). Then we will deal with those devices that fail the test (or are relatively poor).
For devices that fail the functional online test, some test instruments also provide a less formal but more practical treatment method: Because the power of the test instrument to the circuit board can also be applied to the device's corresponding power supply and On the ground pin, if the power pin of the device is edge-cut, this device will be disconnected from the circuit board power supply system.
At this time, perform an online function test on the device; because other devices on the circuit board will not be powered on, the interference effect is eliminated. The actual test effect at this time will be equivalent to "quasi-offline test", and the accuracy rate will be greatly improved.
3. Use ASA-VI curve scan test to compare and test devices not covered by the test library
Because ASA-VI intelligent curve scanning technology can be applied to the comparison test of any device. As long as the test clip can hold the device, there is another reference circuit board. Through comparative testing, the device also has strong fault detection and judgment capabilities. This function makes up for the constraints of the insufficiency of the device test library during the online function test of the device, and expands the detection scope of the test instrument for the failure of the circuit board.
In reality, there are often situations where a good circuit board cannot be found for reference. Moreover, the circuit structure of the board to be repaired does not have any symmetry. In this case, the ASA-VI curve scan comparison test function will not work well. However, due to the incompleteness of the device test library for online function testing, every device on the circuit board cannot be tested again, and the circuit board still cannot be detected. This is the limitation. Just like there is no cure for all diseases.
Four, move first
Because for the time being, only online testing and static characteristic analysis of the devices on the circuit board can be performed. Therefore, whether the faulty circuit board is finally repaired completely must be replaced on the original equipment for inspection. To get the correct result of this inspection process, to determine whether the circuit board is repaired. At this time, it is best to check whether the power of the device is correctly supplied to the circuit board as required, and whether all interface plugs on the circuit board are connected properly. Be sure to exclude the influence of the surrounding environment of the circuit board and the incorrectness of the peripheral circuits, otherwise the work of repairing the circuit board will be led astray!