Maintenance of circuit boards by VFD (Variable-frequency Drive) maintenance instrument

To repair a relatively unfamiliar circuit board without any schematic diagram, the so-called "experience" in the past is difficult to accomplish. Although people with solid hardware skills are full of confidence in repairs, if the method is not appropriate, the work will still be half the effort. So, what can be done to improve maintenance efficiency? According to the statistics of our company's imported equipment maintenance center, the following principles should be followed step by step and in an orderly manner.

Principle 1: Look first and measure later

Tools used: multimeter, magnifying glass

When holding a circuit board to be repaired, it is a good habit to first inspect it visually, and use a magnifying glass if necessary. What do you see?

Mainly look at:

1. Whether there is a disconnection;

2. There is a disconnection phenomenon in the force component such as resistors, electrolytic capacitors, inductors, diodes, and triodes;

3. Whether the printed circuit board connection line on the circuit board is broken or stuck;

4. Has anyone repaired it? Which components have been moved? Whether there are operational errors such as virtual soldering, missing soldering, and reverse insertion;

After confirming that there are no above conditions under repair, first use a multimeter to measure the resistance value between the power supply and ground of the circuit board. Usually the resistance value of the circuit board is 70-80? Above, if the resistance value is too small, only a few or a dozen ohms, it means that there are components on the circuit board that have been broken down or partially broken down, and measures must be taken to find out the broken down components. The specific method is to supply power to the board to be repaired, and touch the temperature of the components on the circuit board with hands, and the lecturer will focus on suspecting the hot hands. If the resistance value is normal, use a multimeter to measure the component components such as resistors, diodes, transistors, field effect tubes, and dial switches on the board. The purpose is to first ensure that the measured components are normal. Our reason is that it can be used A multimeter solves a problem, don't complicate it.

Principle 2: First the outside and then the inside

Tools used: HY circuit online maintenance instrument

If the situation permits, it is best to find a good board that is the same as the board being repaired as a reference, and then use the dual-bar VI curve scanning function to compare the good and bad of the two boards. The initial comparison point can start from the port , and then from the surface to the inside, especially the comparative test of capacitance, can make up for the shortcoming that the multimeter is difficult to measure whether there is leakage online.

Principle 3: Put the easy before the difficult

Tools used: HY circuit online maintenance instrument, electric soldering iron, marker pen

In order to improve the test effect, before the online functional test of the circuit board, some technical processing should be done on the repaired board to minimize the negative impact of various interferences on the test process. The specific measures are:

1. Preparation before the test

Short circuit the crystal oscillator, and solder a leg of the large electrolytic capacitor to make it open, because the charging and discharging of the capacitor can also cause interference.

2. Use the method of elimination to test the device

During the online test or comparison of the devices, please directly confirm the test results for the devices that pass the test (or are relatively normal) for recording; if the test fails (or is relatively out of tolerance), you can test it again. If you pass, you can also confirm the test results first, and continue testing like this until the devices on the board are tested (or compared), and then go back to deal with those devices that failed the test (or are relatively out of tolerance). For devices that have not passed the functional online test, the instrument also provides an unconventional but more practical treatment method. Since the power supply from the instrument to the circuit board can be applied to the corresponding power supply and ground pin of the device through the test clip, if the device is If the power pin of the circuit board is cut with a blade, the device will be separated from the power supply system of the circuit board. At this time, the online function test of the device will be performed. Since other devices on the circuit board will no longer interfere, the actual test effect is equivalent to "quasi-offline" ", the accuracy rate will be greatly improved.

3. Use the ASA-VI curve scan test to conduct comparative tests on devices not covered by the test library

Because the ASA-VI intelligent curve scanning technology can be applied to the comparison test of any device, as long as the test clip can clamp the device, and there is a reference board, through the comparison test, it also has a strong fault detection ability for the device. This function makes up for the insufficiency that the online functional test of the device is subject to the test library, and expands the detection range of the instrument for circuit board faults. In reality, it often happens that a good board cannot be found as a reference, and the circuit structure of the board to be repaired does not have any symmetry. In this case, the ASA-VI curve scanning comparison test function does not work, and the online function test Due to the incomplete device test library, it is impossible to test every device on the circuit board, and the circuit board still cannot be repaired. This is the limitation of the circuit online maintenance instrument, just like there is no cure for all diseases.

Principle 4: Be still before moving

Since the circuit online maintenance instrument can only perform functional online testing and static feature analysis on the components on the circuit board at present, whether it is completely repaired or not must pass the whole machine test and inspection. Therefore, it is best to check whether the power supply of the equipment meets the requirements during the inspection. properly supplied to the board.