We mentioned a simple method to do PCB board repair step by step in the last post - How to Repair Circuit Boards in Yourself?. However, many times bugs cannot just be covered by steps.
Today let's talk about some usual tips for PCB board repair, the theories of which have been proved by plenty of experience, expected to guide you do better in DIY PCB board repair.
Let's Start It from Those That Will Kill Your PCBs
1. Physical Damage
The most common damage to PCB, which often happen to the assembled components. This may be related to physical stress or shock. In rare cases, the main PCB may also be damaged by severe impact or falling from a height.
Diagnosis and Repairing
It can be either uninstalling and replacing the damaged parts or remanufacturing the whole electronic boards, which depends on the damage situation.
When you get PCB board damaged, it is necessary to require the provider to redo the board manufacturing and PCB assembly.
2. Component Failure
Another of the most common causes of printed circuit board failure. If no physical damage but the electronics cannot run, you can almost define the certain parts on the boards are going wrong. The damaged components can be a diode, triode or IC (commonly).
Diagnosis and Repairing
You can easily uninstall and replace the dead components if some diagnosing (voltage/current) tools can work together with your soldering experience.
Otherwise, go for help from your PCB manufacturer or repairers.
3. Trace Damage
Usually, you can see the copper/silver traces on an electronic board with the naked eye, but this is not always the case. If the trace is damaged, the board would not able to run or lost features.
Some common causes of trace damage include lightning strikes, power surges or short circuits, metal dust contamination, overheating, wear, and tear.
Diagnosis and Repairing
If the traces are not very thin and difficult to see, you can usually identify the damage by scanning. The traces are usually bright and shiny in nature, which makes it easier to identify when a break or damage has occurred.
You only need to make up the broken circuit using copper, which will make the current re-flow in the circuitry. Check out our another related article to learn how to do that step by step.
4. Unreasonable Design
Although we are happy to praise every developer' effort but doesn't mean there are no unreasonable layouts. Sometimes, for whatever reason, the developers might cut corners when designing a board or making the necessary components. This can lead to poor design and construction of the board, which will bring in failures on PCB.
Diagnosis and Repairing
This is almost the non-reversible error that will damage your circuit boards, again and again. The most obvious symbolize of an unreasonable design is the number of failures or problems after extended use.
In such cases, you can first ask the senior engineers or repairers for advice, sometimes you need to make an early decision for re-design and manufacturing.
Some Practical Methods to Do PCB Board Repair
1. Visual Inspection
By looking closely, smelling, to identify whether the circuit board has burnt parts, damaged copper, or peculiar smell, whether there is a bad soldering place or a phenomenon of mold and blackness on the interfaces/gold fingers?
Recall the failure phenomenon and the process of failure. In most cases, you'll able to define the failures of certain parts.
2. Overall Inspection
Detect all the components, and replace the defective components to achieve the purpose of PCB board repair. If the components that cannot be detected by the instrument are encountered, this method is adopted, that is, the new components are replaced regardless of whether they are damaged or not. In the end, all the devices on the board are guaranteed to be good.
The method is simple and effective, easy to get started, and the technical level of the engineer is not high, but the operation requires a high degree of care and responsibility.
In addition, this method is powerless for problems such as via failure, copper breakage, and improper adjustment of the potentiometer, it also cannot be used when some chips have programs and data inside.
Contrast method is one of the most commonly used methods for PCB boards repair without drawings. Practice has proved that it has very good effect. By comparing the good board with the defective one, the abnormality is found by comparing the curves of the nodes of the two boards.
However, many times we don't have a good board to compare, but this does not mean that we can't use this method. For example, we can find circuits with the same properties in the board, such as a board with three identical interfaces. The three interfaces have the same circuit, and we can just compare their curves to determine the problem.
When we can't find the situation mentioned above, we can still find the circuit of the common attribute. For example, the bus in the circuit usually has the same curve. Sometimes we can't judge whether an IC is damaged. We can also use the curve scan method to compare the curve with a good IC to achieve the purpose of judgment.
4. Status Inspection
This method is to check the status of normal operation of each component. If the status of a component does not match the normal state, the device or its affected component has a problem. For example, when we check the CPU, we will check if the crystal oscillator is working properly. We can also forcibly push up or down the level of the logic gate and determine whether the output level conforms to the logic of the chip, thereby judge whether the chip is good or bad.
Status inspection is one of the most accurate methods for PCB board repair, which requires a wealth of theoretical knowledge and practical experience, it is a little bit difficult for junior engineers.
Replace all ICs with new ones until they get repaired. Nowadays ICs are getting cheaper and cheaper, like the 74 series and 4000 series chips are less than $0.2/piece cheaper. If you cannot define the IC failure, replace them with new chips. This method I personally feel is a helpless move, it depends entirely on luck rather than effort, even if it really get repaired, you'll don't know where the fault is.
However, this method still has its merits. If a circuit board can be tried to repair on the spot and verify its functions, you can just go this method - replace the ICs one by one, to quickly repair the board.
Another fatal problem with this method is that you must ensure that the IC you bought is not NG. If you accidentally encounter a bad IC during purchase, this will not only repair the fault but will increase the difficulty of PCB board repair.
6. Principle Analysis
The method is to analyze the working principle of a circuit board. Some simple circuits, such as switching power supplies, can be understood by the engineers without schematics.
However, for some relatively complicated and rare equipment, there is no ready-made schematic reference. It can be reverse-engineered by hand to draw the schematics and do PCB board repair following the schematic, which should be the most advanced and accurate method.
This method requires engineers to invest a lot of patience and careful work attitude to complete, one effort can be permanently benefited, but whether or not this method is adopted depends on the value and quantity together with the difficulty of doing the PCB board repair.
3 Grades of PCB Board Repair Engineers
Grade 1 Junior Engineer
They've got the basic circuit theories, are able to recognize different components and do somewhere simple PCB board repair. These people need more practical experiences.
Grade 2 Senior Engineer
These ones have got many experiences, and improved their PCB board repair skills, especially in the repairing speed. They are able to draw the schematics and do somewhere modification.
Grade 3 The Master
At this stage, they have gained enough theoretical knowledge and practical experience, with own innovation, they always seasoned find and solve the problem from the root up. A lot of authoritative technical articles about PCB board repair are written by them.
Which position are you in now?
PS Electronics doesn't often do PCB board repair, because they have put a lot of efforts into materials purchasing and manufacturing management optimizing, which reduced the PCB failure rate significantly.
If you don't want to spend time on PCB board repairs, it is okay to ask them to quickly deliver some high-quality alternatives.
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