I was operating a B747-300 many moons ago on a domestic flight of about 1 hour duration. Shortly after TOC (i.e. shortly before TOD) there was an acrid smell and much stinging of eyes. We went through all the prescribed items and managed to convince ourselves that the smoke had stopped - in retrospect I think we had just got used to the stinging and sense of smell deadened ....
In the meantime we had expedited descent into our destination airport and fire services waiting.
Passengers were fast tracked off the aircraft - not evacuated - and the engineers started hunting for the source. (By this time it was clear that the smoke was NOT a figment of the imagination!)
After some time we narrowed it down to aft pedestal and radios / INS removed which confirmed the area but no actual fire.
The first class ceiling panels were removed and revealed a seriously blackened / melted autothrottle motor and wiring ..... circuit breaker was still firmly in place!
It's not a nice feeling but what I do remember is how much I wanted it NOT to be a fire and how quickly my eyes and nose adjusted and helped me arrive at the conclusion that all was under control.