Repairing unfamiliar and complex faulty boards without a schematic is a challenging task. Even highly skilled service professionals, with a wealth of experience and in-depth knowledge of electronics, are not up to the task with intuition and so-called "service experience". While they may be confident in their repair work, if they don't do it right, they will still be less effective and inefficient. In this way, we need to standardize the maintenance idea.
First, look first and then measure.
The first step in dealing with a circuit board that needs to be repaired should be a visual inspection, or a magnifying glass for a closer look if necessary. Specific aspects of the examination include:
1.Whether there is a broken wire or short circuit on the circuit board, especially to observe whether the connecting wire of the printed board is broken, adhered and other phenomena;
2.Check whether the relevant components, such as resistors, capacitors, inductors, diodes, transistors, etc., are disconnected or damaged;
3.Verify whether the circuit board has been repaired by others, if so, you need to understand the specific repair content, check whether there are problems such as false soldering, missing soldering, and reverse insertion.
After the above observations are made, a multimeter should be used to measure the resistance between the power supply and ground of the board. Under normal circumstances, the resistance value of the circuit board should not be less than 70. If the resistance value is abnormally low, it may mean that there is a breakdown or partial breakdown of the component on the board. At this point, further steps need to be taken to locate and repair the broken down component. An effective way to do this is to power up the board and measure the temperature of each device using a spot thermometer, with abnormally high temperatures as a key suspect.
If the resistance value is normal, the next step should be to use a multimeter to measure the components such as the resistance vessel components, diodes, transistors, MOSFETs, and toggle switches on the board to ensure that they are working properly. In this process, general testing tools (such as multimeters) should be prioritized for troubleshooting to avoid unnecessary complications.
Second, first the outside and then the inside.
In order to ensure the accuracy and reliability of the test results, it is recommended to use a circuit board that is exactly the same as the board to be repaired and is working properly as a reference standard when using the circuit repair tester for inspection. Subsequently, by using the tester's two-bar VI curve scanning function, the two boards can be tested in detail. It is advisable to start the test at the port of the board and work your way up to it, with a special focus on comparative testing of capacitors. This can make up for the lack of difficulty in accurately judging whether the capacitor is leaking during the detection of the multimeter**, thereby improving the accuracy of fault location and maintenance.
Third, the easy first and then the difficult.
In order to achieve better test results, specific technical treatments must be performed on the board to be repaired before the functional test of the circuit board is carried out during the testing process using the circuit repair tester to minimize the impact of various potential interferences on the test process. The detailed technical operation steps are listed below:
1.Preparation for the test.
It is required to short-circuit the crystal oscillator (it is necessary to distinguish the signal output pins of the four-pin crystal oscillator, only these two pins should be short-circuited, and the other two pins are used as power supply pins, and short circuits are prohibited). For large-capacity electrolytic capacitors, it is necessary to solder them to open the circuit, because the charging and discharging process of large-capacity capacitors may also cause interference.
2.Test strategy for the device.
When performing ** or comparative tests on a device, the test results should be immediately confirmed and documented for devices that pass the test (or are relatively normal). If the test fails (or the comparison result is out of tolerance), it is recommended to repeat the test once. If the result still fails, the test result is also confirmed. This testing process is continued until all devices on the board have been tested. Subsequently, devices that fail the test (or compare the results are out of tolerance) are processed.
In the event of the failure of some test instruments in the event of the failure of the functional test device, it also provides a slightly informal and practical emergency strategy for actual operation. Such a test instrument provides power and ground to the devices on the board via a test clip. Once the power pin of the device is bladed, the device is detached from the board's power supply system.
Subsequently, the device is tested again. Since the other devices on the board do not receive power** at this time, potential interference is eliminated. Therefore, the test effect at this time is close to the "quasi-offline test", which greatly improves the accuracy of the test.
3.Application of ASA-VI curve scan test.
ASA-VI intelligent curve scanning technology has the ability to perform comparative tests on any device. As long as the test clip is able to hold the device and there is a reference circuit board, the technology can accurately test and judge the device's performance and potential failures. This strategy is not limited by the coverage of the components in the test library, which greatly improves the scope of fault detection.
However, in practice, it may be difficult to obtain a suitable reference board, or the circuit structure of the board to be repaired is not symmetrical, in which case the functionality of the ASA-VI curve scan test may be limited. On the other hand, if the device library for functional testing is incomplete, it is impossible to comprehensively test all the devices on the circuit board, which also constitutes the limitation of the circuit repair tester. Just as there is no one-size-fits-all drug, the circuit repair tester also has its scope of application in use.
Fourth, first static and then moving.
Given that the Circuit Repair Tester is currently limited to functional testing and static characterization of devices on the board, testing and verification in the actual equipment environment is necessary to determine whether a faulty circuit board has been fully repaired. Before performing this inspection, it is important to ensure that the proper supply of the power interface on the original device and that the various interface inserts on the board are properly connected. At the same time, it is necessary to exclude the possible interference factors in the surrounding environment and peripheral circuits of the circuit board, so as not to mislead the maintenance work and ensure the accuracy of the circuit board maintenance.