Defects and component malfunctions are common occurrences in the PCB industry. Circuit boards may exhibit different behavior than expected due to improper soldering or placement of components, damage due to overheating, and more. Such behavior can cause the circuit to work poorly or completely stop functioning. Fortunately, there is no need to worry as there are some simple ways to troubleshoot a PCB to identify, verify, and test the problematic areas and components.
Although troubleshooting PCBs is difficult due to factors like signal analysis, the number of layers, and the complexity of components, it’s achievable with the right type of electronic equipment. The most important tool is a multimeter, but you may also need a logic analyzer, power supply, oscilloscope, and an LCR meter to analyze the operational behavior of the board’s circuits. Whether you are a contract electronics manufacturer or a third-party electronics retailer, it can help to learn how to troubleshoot a printed circuit board.
(Pixabay / ranjatm)
Troubleshooting a PCB: Do You Need to Map?
The troubleshooting techniques we’ll see shortly are applicable on single layers, rigid/flex, digital analog, and radio frequency PCBs. But first, you’ll need to map out a PCB. This requires you to develop a clear understanding of its traces, signals, and current flow. Plus, you need to have the knowledge of which capacitor-resistor pairs are ideal to proceed with troubleshooting.
It will also help if you have a good grip on the filter, chole, and voltage divider position in the circuit board. However, suppose you don’t have a solid understanding of the configuration. In that case, it’s ideal to start the troubleshooting process from the connectors – the interface through which erroneous external inputs make their way into the circuit board. That said, you have to be good at mapping a PCB to continue without accessing the board’ schematics. This could eat up a lot of time, as every solder joint will need to be tested using a multimeter probe.
A better, more natural way to trace out PBCs is to use an aluminum piece. This method enables you to search for connections over a broader area per time, reducing the amount of effort and time involved. The process requires a piece of aluminum foil, a wire cutter, crocodile wire clips, and multimeter.
Pro tip: Instructables has an excellent tutorial on how to identify and trace PCB tracks through this technique quickly.
After mapping out your PCB, you can move onto the troubleshooting part.
Start with a Visual Inspection
This step uncovers the obvious issues, such as burnt-out components, overlapped through-hole, missing components, and signs of heating. It’s typically challenging to spot components burnt from excessive current, but the smell or a magnified visual inspection can indicate the damaged component’s presence. Additionally, keep an eye out for bulging components, as they also indicate the presence of an issue – especially for electrolytic capacitors. Moreover, look for touches or the shorts on the ‘adjacent’ soldered points. If any of these things requires a repair, you can go with an action like replacing the components with new ones or desoldering the shorted parts. See any lousy solder joints? This may be indicative of a ‘dry’ joint that could alter the circuit’s conduction.
Then Inspect Physically
If you don’t find anything off with the visual inspection, proceed with a. physical inspection by exerting power on the circuit. You can identify the problem areas by touching the surface of the PCB, along with its components. This technique modifies the system’s behavior and can help you trace out components that require more capacitance. Use compressed canned air to lower the temperature on the hotter components so that you can test the circuit’s mechanism.
Pro tip: Make sure to touch the printed circuit board one hand at a time. This is important for avoiding electrical jolts that could result in a fatality. Try keeping one hand in the pocket as you touch the live circuit. Alternatively, block out the potential paths for the current to travel to the ground to keep shocks at bay.
Integrated Circuit (IC) Analysis
Checking integrated circuit components is always challenging. While you can identify them by their markings and conduct operational testing using logic analyzers and oscilloscopes, specialty ICs in different PCB designs and configurations make these challenging to test. A handy technique is to compare the circuit’s behavior to a familiar good circuit, which should help you detect anomalous behavior on the circuitry.
Test Component by Component
Lastly, you can engage in discrete component inspection, where you sharply test every PCB component individually. This requires you to use the tools discussed earlier. Using a multimeter or LCR meter, you can test the ‘piece by piece’ value of a resistor, transistor, LED, capacitor, and the remaining active components. The components are in a good state if they register equal to or less than the stated component value. A higher value indicates that either the solder joint or the component is bad. While performing discrete testing, make sure to use the multimeter’s diode testing mode to check the transistors’ and diodes’ health.
You should essentially check the behavior of the base-collector and base-emitter junctions of a transistor, which should function like discrete notes and conduct in a single direction with a similar voltage drop. Another technique for unpowered testing of components is nodal analysis. This involves applying power to a single component and then measuring its current V/I (voltage vs. current) response.
Compared to other techniques, nodal analysis systematically measures the voltages at certain nodes to compare with the reference node voltage (this node is randomly selected from the board’s various nodes). Then a KCL equation is applied to identify the difference between the node voltages in branch currents terms.
These are some of the ways you can troubleshoot a PCB for component defects and other issues. The right technique for you will depend on the complexity of your PCB and your industry experience. If you lack the expertise or tools to troubleshoot a printed circuit board, you can contact a professional to do it for you without damaging the integrity of your board. As a leading full-service electronic manufacturing service, we’re here to help you with the full range of your company’s PCB-related needs.