When using a thermal camera for PCB surveys I consider the following.....
1. Is there any component getting hotter than would normally be expected ? If so why ? Overload, internal failure or poor design.
2. Is(are) there any component(s) not getting as warm as expected in normal operation ? Failed/missing supply, not enabled, internal failure.
3. Hot capacitors ? Never a good sign in general use and worthy of investigation. ESR and look for leakage.
4. Hot connectors ? Often a sign of corrosion/arcing of poor design (under rated contact surfaces)
5. Hot spots on large IC's ? This is normal for many IC's but can be a sign of trouble in those that are not functioning properly.Often offset from the centre and an internal power component failure.
6. Are similar component srunning at similar temperatures? If not why not ? This may be absolutely normal depending upon the components tasking but in a group of the same IC, they often have similar dissipation. e.g. RAM IC's and buffer IC's
7. In the case of a supply rail short and a need to find the cause..... use lab PSU with correct voltage set but higher current capability to supply the shorted power rail. The thermal camera can then image the PCB track supplying the shorted component. Often the PCB track and failed component will glow brightly compared to the background temperature if 1A is passed into the shorted track. Care is needed to not overload the PCB track. Lower currents are also effective by refrigerating the PCB to 5C before this test improves visibility of the PCB track and failed component at lower drive currents. If the component is dead short and does not heat up, the PCB track literally leads you by the nose to that part. Use the lowest current that works when doing this test to avoid stressing the PCB too much.
8. Temperature of air leaving the cooling ports of an equipment ? Elevated temperatures at this exit port indicate trouble within. Such can be caused by blocked intakes/air filters, dust and dirt accumulation in fan radiators, overloading, overheating power components and underated heatsinks. If an equipment is checked over its operating life, the user can see any evidence of degradation in cooling performance, or overheating of internal parts. Good preventative maintenance.
Just a few pointers from my experience.
Fraser