Maybe someone used no-rosin flux for touching up some joints and then sprayed flux-cleaner on it instead of water.I came across this this today, and I was wondering what caused this. The circuit is outside, but in a casing so it will not get wet by rain or water. The casing is not waterproof or air tight.
It looks like the circuit has started to corrode or grow mold.
View attachment 75246 View attachment 75247
Could it be something other than water/moisture?