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PCB Repair – Only Mostly Dead

The iconic line from The Princess Bride holds true when it comes to electronic repair and PCB repair: there’s a big difference between mostly dead and all dead. And often it just so happens that your circuit board is only mostly dead.

How can electronics that look so badly damaged be repaired and made fully functional again? 

There are a lot of factors to consider when approaching this kind of PCB repair, but broadly they can be put into two groups: understanding how electronic components fail, and understanding how they actually function in the circuit. 

Knowledge of the modes of failure for different electronic devices is critical to be able to assess the extent of the damage. How a component breaks down depends not only on the type of electronic device it is but also on its manufacturing technology. For example, a tantalum capacitor on a circuit board will fail short whereas an electrolytic capacitor will fail open, even though their voltage and capacitance ratings may be identical. And the mode of failure will also impact each of the other devices that are connected to it – often causing electrical damage even without any visible physical damage.

It’s also important to note that the printed circuit board itself is a component which can be broken and repaired. Traces can be severed, burned, corroded, or blown right off the board. The FR-4 fiberglass/epoxy base of PCBs can be badly charred, turning black in appearance and flaking apart. Just as burned FR-4 no longer has the same physical properties, it also loses its key electrical property: high dielectric strength. This means that it no longer acts as an insulator and can break down and short other traces on the board. Even if a burned section of a PCB tests high resistance when using a standard multimeter, it’s more likely to break down at high voltage and can be dangerous if left in when the board is powered up again. 

The damages to circuit board traces outlined above – those that cause shorts, and those that are open – can completely change the connections in a circuit. How can these be detected and corrected?

What makes it possible is understanding how the circuit as a whole works. Not the same as fully reverse engineering the PCB, this is a more informal process; it synthesizes knowing how the whole electronic device works and being able to read a circuit board. What are the inputs and outputs? Where is the power? What different voltages should be present on the board? Where are the signals, and what is doing the processing/controls? These are all things that can be determined from factors like topology, component ratings, physical sizing, and creating a circuit board schematic. By comparing the actual test results on the damaged circuit board with the theoretical circuit to achieve the desired function, it’s possible to locate and fix otherwise hidden issues.

Ultimately, PCB repair can be possible even in cases where components have failed catastrophically. There’s many times where a circuit board is only mostly dead. And it can be fixed – no wizardry required – by applying understanding of electrical theory and practical experience repairing electronics.

If there’s a circuit board or electronic device that you are still unsure about, and would like to get it evaluated to see if it is repairable, please contact us directly at  ENA specializes in circuit board repair and pcb reverse engineering, including capabilities to remanufacture and clone PCBs.

Posted in Industrial Repair, PCB Reverse Engineering

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