Are you repairing somewhat older Japanese (Yamaha, Nikko, etc.) equipment, but the problem seems very obscure?
In some amplifiers and other equipment, the supply capacitors and other large pcb-mounted devices are secured in place by a type of gluelike substance, that after several years causes corrosion to all metal parts that it touches; eventually, the metal connections (like component wire leads and wire bridges) will fail. The substance in question is a dark yellow rubber-like compound, coloring brown and turning rather hard on the places where damage is done to other components. The only solution is to scratch it away completely and replace all components affected. I’ve already repaired five amps where this turned out to be the cause of trouble – with very vague symptoms, like a missing ground reference to an endstage, an on-board controller that wouldn’t start up, etc. The first time it took me forever to find, so if this posting will make even one repair easier for someone, I’m already happy. Hope this makes life a (little) bit easier for all those people out there trying to repair stuff
