From what the OP has reported of this PCB’s fault, a particular PCB track has been identified as faulty with a short.
In such cases it is unwise to strain the power supply that normally feeds the PCB in case long duration over current is involved with negative effects on the regulators. I would approach such a fault with a Toneohm equipment but that is not the suggested MO of the OP. If using a thermal imaging based short tracing technique I would connect a lab power supply to the failed PCB track and the track to which it is shorted. I would apply a voltage of around 1V but set the current limit to something reasonable that will not damage the PCB track. 1A should be safe unless the PCB tracks are very thin. The lab power supply will continue to pass 1A through the PCB shorted track rather than fold back and shut down, as some equipment power supplies do. As such heat will be created in the PCB track and is easily seen with a thermal camera. Most thermal cameras can achieve a Delta T sensitivity Of better than 0.1C so the heating effect will be detectable. In some cases it may be necessary to carefully increase the current flow but that is often only needed for very challenging high layer count PCB’s and must be done with care. If the PCB gets too hot around the area of interest and thermal spread blurs the source, just cool the PCB in the fridge, freezer or using Freezer spray. Once cold, repeat the current induced heating test.
The PCB track path between the lab power supply input connections should be relatively obvious and any failed component or track insulation identifiable. It is not always so easy however, especially on a new PCB that failed production testing. A failed feed-thru under a VLSI chip or through hole connector can be a challenge ! Life is made a lot easier I’d a schematic is available for the PCB to identify components and connection nodes on the track of interest.
A thermal camera is quite an investment so I advise caution when shopping at the budget end of the market. Do not be fooled by some sellers offering deals that are too good to be true, as often they are ! Very low resolution plus masses of interpolation is not a wise camera choice for PCB work.
FLIR do offer reasonable cameras that use the Lepton but they are a compromise solution so suffer from relatively high image noise content and need a close-up lens for PCB work. Such a lens is just a $20 CO2 laser focus lens and is needed by many fixed focus cameras for PCB work at less than 30cm distance.
Now, given a choice, I would personally buy one of Bills Raytheon Thermal Eye 2000AS cores that produce lovely monochrome images of 160 x 120 pixels using a quality Germanium lens and Raytheon quality electronics with its built in image processing to provide good images. Such a core can be up and running in mere minutes and providing excellent images on a TV or dedicated composite video NTSC monitor. For £160 they are a bargain. The FLIR budget cameras are far more ‘sexy’ and a complete camera solution. The Lepton core is ‘OK’ but do not expect too much from it. The Lepton 3 160 x 120 pixel based cameras are the minimum specification I would recommend for PCB work at close range using a Supplemental close-up lens providing 100mm working distance.
Fraser