4 "Rules" to Follow when Repairing an Unfamiliar Circuit Board

In the absence of any schematic condition to a relatively unfamiliar circuit board maintenance, the so-called "experience" is difficult to act, although the hardware of the deep foundation of the people are full of confidence in maintenance, but if the method is not appropriate, the work is still half the result. So, what can be done to improve maintenance efficiency? According to the statistics of our company's imported equipment maintenance center, the following steps should be followed in an orderly manner.

Method 1: Look before you measure

Tools: multimeter, magnifying glass

When holding a circuit board to be repaired, a good habit is first to deal with its visual inspection, if necessary with the aid of a magnifying glass, see what?

Mainly look at:

1, whether there is a broken line;

2, component components such as resistance, electrolytic capacitance, inductance, diode, transistor and so on when there is disconnect phenomenon;

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

4. Has anyone ever repaired it? Which components have been moved? Whether there are faults in operation such as virtual welding, missing welding and reverse plugging;

After determining to be repaired without the above condition, first use a multimeter to measure the resistance value between the circuit board power supply and the ground, usually the resistance value of the circuit board are 70-80? Above, if the resistance value is too small, only a few or a dozen ohm, that there are components on the circuit board breakdown or partial breakdown, it is necessary to take measures to find out the components of the breakdown. The specific way is to be repaired board power supply, touch the temperature of each device on the circuit board by hand, hot lecturer key suspect object. If the resistance value is normal, use a multimeter to measure the plate on the resistance, diode, triode, field effect tube, dial switch and other components, its purpose is to first ensure that the measured components are normal, our reason is, can use a multimeter to solve the problem, do not complicate it.

Method 2: Outside-in

Using tools: circuit online maintenance instrument

If the situation allows, it is best to find a good board as a reference board to be repaired, and then use the VI curve scanning function of the two boards for good and bad contrast test, the starting point of comparison can start from the port, and then from the surface to the inside, especially for the capacitor comparison test, can make up for the multimeter online difficult to measure whether leakage deficiencies.

Method 3: Easy before hard

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

In order to improve the test effect, some technical treatment should be done before the online functional test of the printed circuit board, so as to minimize the negative impact of various interference on the test process. The specific measures are:

1. Preparation before the test

Short circuit the crystal oscillator, and weld the next leg of the large electrolytic capacitor to open it, because the charge and discharge of the capacitor can also cause interference.

2. The device is tested by elimination method

During online testing or comparison of devices, confirm the test results directly for the convenience of record if the devices pass the test (or are relatively normal). If the test fails (or is relatively out of tolerance), it can be tested again. If it still fails, it can also confirm the test results and continue testing until the components on the board have been tested (or compared), and then come back to deal with those components that fail the test (or are relatively out of tolerance). For the 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 circuit board of the instrument can be applied to the corresponding power supply and foundation of the device through the test clip, if the power supply foot of the device is cut, the device will be separated from the circuit board power supply system, then the device will be tested online. As other components on the PCB board will not interfere again, the actual test effect is equivalent to "quasi-offline", and the accuracy will be greatly improved.

3. Compare and test devices not covered by the test library with ASA-VI curve scanning test

As 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, there is a reference board, through the comparative test, the device also has strong fault detection ability. This function makes up for the insufficiency of the device online functional test subject to the test library and expands the scope of the instrument to detect the fault of the circuit board. In reality, it is often impossible to find a good board for reference, and there is no symmetry in the circuit structure of the board itself to be repaired. In this case, ASA-VI curve scanning comparison test function can not play a role, and online functional test can not complete the test of every device on the circuit board due to the incomplete device test library, the circuit board is still unable to repair. This is the limit of the online circuit repair device, just as there is no cure-all.

Method 4: Quiet before moving

Because the circuit online maintenance instrument can only carry out functional online testing and static characteristic analysis of the devices on the circuit board at present, whether it is completely repaired must be tested and inspected by the whole machine. Therefore, it is best to check whether the power supply of the equipment is correctly supplied to the PCB circuit board according to the requirements in the inspection.