See me, feel me, hear me
With so much electronic test equipment available that’s affordable and easy to use it’s easy to forget the fantastic ability of us e-engineers to interact with (faulty) electronics using just one’s senses and no equipment or apps at all.
I’m sure I am not alone in being able to smell out (literally) serious trouble in a circuit without access to a 6-digit ammeter with USB 3.0 and IoT connectivity. Even with the equipment switched off, certain parts that have run hot — and may be the cause of the trouble — produce a smell ever so light. Besides component failures, also be ready to identify your big fat design mistakes like the 1 ohm resistor where 1 k was required. Okay, it does help if the parts have signs of burning, scalding, glazing or micro explosion but the light smell alone should be strong enough especially if a part is in a well enclosed case which you open for the first time. Amps can be smelled, just as solder flux, hot pertinax, and dust.