PCB News - Rules to follow when repairing unfamiliar circuit boards

Circuit board manufacturers: 4 "roads" that must be followed in the repair of unfamiliar circuit boards

To repair a relatively unfamiliar circuit board without any schematic diagrams, the so-called "experience" in the past is difficult to accomplish. Although people with deep hardware knowledge are confident in repairing, if the method is improper, the work will still get half the result with half the effort. So, what can be done to improve maintenance efficiency? According to the statistics of the imported equipment maintenance center of our company, the following steps should be followed in an orderly manner.

Method 1: Look first and then measure
Use tools: multimeter, magnifying glass

When holding a circuit board to be repaired, a good habit is to first visually inspect it, and use a magnifying glass when necessary. What should you look at?
Mainly look:

1. Whether there is disconnection;

2. There is a disconnection phenomenon when the component of force, such as resistance, electrolytic capacitor, inductance, diode, triode, etc.;

3. Whether the printed circuit board connection line on the circuit board is broken, sticking, etc.;

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

After confirming that the above-mentioned condition has not been repaired, first use a multimeter to measure the resistance between the power supply and the ground of the circuit board. Usually the resistance 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 repaired board, touch the temperature of the components on the circuit board by hand, and the hot lecturer focuses on the suspect. If the resistance value is normal, use a multimeter to measure the resistance, diode, transistor, field effect tube, dial switch and other force components on the board. The purpose is to first ensure that the measured components are normal. Our reason is that it can be used. Don't complicate the problem that the multimeter solves.

Method two: first outside and then inside
Use tool: circuit online repair instrument
If the situation permits, it is best to find a good board that is the same as the repaired board 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 be from the port., And then from the table to the inside, especially the comparative test of the capacitance, it can make up for the shortcomings of the multimeter that it is difficult to detect the leakage of electricity online.

Method three: easy first and difficult later
Use tools: circuit online repair instrument, electric soldering iron, marker pen
In order to improve the test effect, before the online function 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 pin to open the large electrolytic capacitor, because the charging and discharging of the capacitor can also bring interference.

2. Use the elimination method to test the device

During the online test or comparison of the device, if the device passes the test (or relatively normal), please directly confirm the test result for recording; if the test fails (or is out of tolerance), you can test it again, if it still fails Pass, you can also confirm the test result first, and continue testing until the device on the board is tested (or compared), and then go back and deal with those devices that have not passed the test (or are out of tolerance). For devices that have not passed the functional online test, the instrument also provides a less formal but more practical processing method, because the power supply of the instrument to the circuit board can be applied to the corresponding power and ground pins of the device through the test clip. If the power supply pin is cut, the device will be separated from the circuit board power supply system. At this time, the device will be tested online. 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 compare and test the devices not covered by the test library

Because the ASA-VI intelligent curve scanning technology can be applied to the comparative test of any device, as long as the test clip can clamp the device, and a reference board, through the comparison test, it also has a strong fault detection capability for the device. This function makes up for the insufficiency of the device's online function test subject to the test library, and expands the instrument's detection range of circuit board faults. In reality, there are often scenarios where a good board cannot be found for reference, and 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 does not work, but 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 repairer, just like there is no cure for all diseases.

Method 4: first static and then move
Since the circuit online repairer can only perform functional online test and static characteristic analysis of the devices on the PCB at present, whether it is completely repaired must be tested by the whole machine. Therefore, it is best to check whether the power supply of the equipment is correct according to the requirements. Supply to the circuit board.