If this method has not been used or mentioned here, this helped me get through to the point of eventual acknowledgement of an BJT's Base requirements for proper Collector operation per devices few years ago when observing them as interesting self functioning toggles before comprehension of where to look for any kind of datasheet or info on the part.
Concepts: Prototyping transistor configured boards for new or large concepts (designs that may be overburdening a transistors current rating, known or unknown). Loose connections and dry welds can happen resulting in commutation (without stator
) SAT fault.
The term that checking temperature as to not overload an transistor by determining heat build up as an if you can not touch it for more than x length of time then it's too hot as per an example I have seen used.
:Cautions: The substance mentioned is applicable to determine if a transistor would be overheating on a board containing multiple numbers far beyond checking them all within a catch it before it burns out method.
The substance would be Soldering Flux in the paste form, a small dab applied to the transistors top (TO-92) or the face (or other types including FETS). All be it potentially messy if Flux is overused (or a rather large number of TTL), as determined by the rough time that it takes to melt, that Flux melting temp is actually quite low,
could be used to determine if the part is going to fail due to overheating meltdown, fast pace Flux melt would highly indicate a potential failure, a slow smelt would state that the transistor is reaching some considerable warmth. Or produce an actual smoke plume of flux vapor that may allow a catch before burnout condition of the part.
The other part of the cautions are on respiratory/Visual concerns, as when dealing with Flux and Solder as with other chemicals are hazards.
A well ventilated area would be recommended.