The repairmen with deep knowledge of electronic skills and hardware are full of determination for repair work. But if the method is not appropriate, the work will be half done. So how can we improve the repair power better?

　　Here are some guidelines to be commented on for peer reference. Make the repair work orderly and step by step

　　Criterion 1: look first, then measure

　　The circuit board to be repaired shall be visually inspected first, and the magnifier shall be used for observation if necessary

　　Mainly see:

　　1. Whether there is any disconnection or short circuit, especially whether there is any crack or adhesion on the connecting line of PCB;

　　2. Whether the related components such as resistance capacitance inductance diode triode are disconnected;

　　3. Whether someone has repaired it? Which equipment has been moved? Whether there are problems such as faulty welding, missing welding, wrong insertion, etc

　　After removing the above situation, first measure the resistance between the power supply and the ground of the circuit board with a multimeter. Generally, the resistance of the circuit board should not be less than 70 Ω. If the resistance is too small, it is only a few or a dozen ohms. It means that measures must be taken to find out the broken down component equipment if there is component equipment on the circuit board that is broken down or partially broken down. The specific method is to power up the repaired board (note! At this moment, it is necessary to find out the component equipment of the board The voltage value and positive and negative polarity of the working voltage shall not be connected wrongly or added higher than the working voltage value. Otherwise, the circuit board to be repaired will be damaged! The old fault has not been eliminated and new defects have been added!!) the temperature of each equipment on the circuit board shall be measured by the point thermometer, and the fast and high temperature rise shall be regarded as the key problem object

　　If the resistance value is normal, then measure the resistance and capacitance devices on the board with multimeter. The purpose is to ensure that the measured devices are normal. If you can use general test tools (such as multimeter, etc.), do not complicate it

　　Guideline 2: first outside, then inside

　　If the situation allows, it is better to have a good circuit board as the same as the board to be repaired as a reference. Then use the dual port VI curve scanning function of the tester to carry out a good and bad comparison test on the two boards. The comparison test point of the beginning can start from the port of the circuit board; Then, the comparison test from the outside to the inside, especially for the capacitor, can make up for the defect that it is difficult for the multimeter to measure the leakage of the capacitor on line

　　Rule 3: easy before hard

　　In order to improve the function of the test, some skill processing should be done to the repaired board before the online function test of the circuit board to minimize the impact of various disturbances on the test process. The specific measures are as follows:

　　1. Preparation before test

　　Short circuit the crystal oscillator (make sure that the four legs of the crystal oscillator are the signal output pins that can be short circuited. Remember that in general, the other two legs are the power pins. Do not short them!!) for large capacity electrolytic capacitors, weld the next leg to make them open. Because the charging and discharging of large capacity capacitors will also cause disturbance

　　2. Test the equipment by sweeping

　　In the process of on-line test or comparative test for the equipment, please directly acknowledge the test results and record the equipment that has passed the test (or is more normal). The equipment that has not passed the test (or is more out of tolerance) can be retested. If it still hasn't passed the test, you can first acknowledge the test results. Such a test can be continued until the equipment on the board has been tested (or compared). Then you can deal with those equipment that haven't passed the test（ Or more out of tolerance) equipment

　　For the equipment without function on-line test, some test instruments also provide a kind of irregular but more useful treatment method: because the power supply of the test instrument to the circuit board can also be applied to the corresponding power supply and ground pin of the equipment through the test clip, if the power supply pin of the equipment is cut, the equipment will be separated from the circuit board power supply system

　　At this time, the online function test will be carried out for the equipment; as other equipment on the circuit board will not be powered on, the disturbance will be eliminated. The actual test function at this moment will be equivalent to the "quasi offline test" accuracy rate, which will make great progress

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