Most engineers and technicians troubleshoot electronic boards with typical tools such as multi-meters, oscilloscopes and other standard test equipment. While this works well for most troubleshooting, sometimes a problem comes along that is very difficult to troubleshoot. Power rail shorts are a perfect example. The reason? Power supplies typically source several integrated circuits, each of which usually has one or more decoupling capacitors. If any one of these components are shorted, the entire circuit will appear shorted. To clarify, a true short would be measured as a zero-ohm reading, but for the purpose of this discussion, shorts also include non zero-ohm measurements, but much less than expected – typically less than 10 ohms.
Once a power rail short is discovered on a board assembly, the traditional troubleshooting technique is as follows:
This can be a very long, and not very cost-effective, method of troubleshooting shorts. An alternate way of troubleshooting boards with power rail shorts is to use a thermal camera.
What you will need:
Procedure:
Possible results:
If any hot spots are found, heat up the metal pointing device between your fingers and point to the hot spot to confirm the component that is visually hot. The overlay image may not be aligned perfectly. Also note the measured temperature in the bullseye on the upper left corner of the screen.
Hot capacitor found (seen in image): This is likely a damaged capacitor that when power was applied developed a short. Remove it to confirm the short is gone. If not, repeat the process as more may have been found.
Warm inductor or ferrite bead found: This may be normal, or it may indicate current flowing through that component. That inductor or ferrite bead is likely okay but may point to a part of the circuit to focus on. Remove it and repeat the thermal camera test looking for additional clues.
A warm area of the board is observed: This is likely due to a solder bridge. The bridge can handle sufficient current so that it is not getting very hot but is warming up. This will usually only be seen at higher tested currents. Inspect the board looking for solder bridges in that area that the board warmed up.
No observable warm or hot spots: This is probably due to a large solder short or a PCB short that can handle all the current and more that you applied. The thermal camera test is not very effective in this situation and standard troubleshooting techniques should be applied.
Additionally, a thermal camera can be used to detect lack of heat where expected, indicating that a portion of the circuit is not powered up or working. As the trusted electronics manufacturer you’ve been looking for, ACDi is committed to delivering the highest-quality printed circuit boards and box-build electronics assemblies. Troubleshooting is part of the product engineering support services that we offer to our clients. Contact us to learn more.
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