Hi John,
We had a FLIR system with interchangeable lenses and good thermal resolution for the time (15 years ago). I see the new ones now at a fraction of the cost which we paid and they have better resolution. Amazing how the infrared imaging technology has progressed. Most suppliers will gladly demo a unit for you which is what I would recommend in your instance.
Bridges under components may take a bit longer to realize where the localized heating is taking place. You can image both sides of the assembly looking for the hot spot which helps if large components are obscuring the direct view of where the short is. This will also ID a component which is electrically shorted from ground to the voltage rail as well.
Place the PCBA and camera in a good steady holding position. Power up the short with current limit of around 10 mA to start with and look for the first area to indicate increased localized heat. You then reposition or zoom in to get finer details. Generally, you can increase current substantially if needed, however too much current could "fuse open" your electrical short which would then be impossible to find the electrical culprit and the assembly would not be reliable.
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