How to repair circuit boards?

How to repair circuit boards ?

Usually circuit board inspection includes the following three levels of inspection:

1) Bare board detection;

2) Online detection;

3) Function detection.

A general-purpose type of tester can be used to test one style and type of circuit board, or it can be used for specific applications.

The following is an online measurement method to explain how to repair the circuit board:

Step 1: Power up the board

In this step, it should be noted that some circuit board power supply is not single, it may require 5V, plus or minus 12V, 24V, etc., do not add the power supply that should be added. After the circuit board is powered on, touch the components on the circuit board by hand to see if there are any hot and hot components, and focus on checking the 74 series chips. If the components are hot, it means that the components may have been damaged. After replacing the components, check that the board failure has been resolved.

Step 2: Measure the gate circuit on the circuit board with an oscilloscope and observe whether it conforms to the logical relationship

If the output does not conform to logic, it needs to be treated separately in two cases. One is that the output should be low level, but the actual measurement is high level, which can directly judge the chip damage; the other is that the output should be high level, The actual measurement is low, and it cannot be judged that the chip is damaged. It is also necessary to disconnect the chip from the subsequent circuit, measure again, observe whether the logic is reasonable, and determine whether the chip is good or bad.

Step 3: Use an oscilloscope to measure the crystal oscillator in the digital circuit to see if it has output

If there is no output, it is necessary to remove the chips connected to the crystal oscillator as much as possible before measuring. If there is no output, it is preliminarily judged that the crystal oscillator has been damaged; if there is output, you need to put the removed chips back one by one, and install one chip to test one to find out the fault.

Step 4: Measure the bus with an oscilloscope and observe whether the signal is normal

A digital circuit with a bus structure generally includes three channels of digital, address, and control buses. Measure the three-way bus with an oscilloscope, compare the schematic diagram, observe whether the signal is normal, and find out the problem.