Juchli Engineering was asked to look at a problem with replacement intercom circuit boards not working. The intercom in question is used by Edmonton Fire and Rescue to communicate between people sitting inside the noisy truck.
These particular circuit boards were manufactured to extend the life of an end-of-life (but still very useful) intercom system, and they were not amplifying audio properly.
A test input signal was traced through the circuit and the problem was isolated to a specific amplifier stage, then to a specific capacitor value.