Hey guys, I've got a APC UPS backup a while ago but have not used it too often. A couple of days ago I turned it on and it was making electrical buzzing noises every few seconds, then pause for a second and then the buzzing noise would repeat. It is loud enough to bother me so I took it apart. I believe it is a transformer that is making this noise but I also hear some very soft chirping sound from a nearby capacitor and both, the chirping and the buzzing, would start and stop at the same time. The capacitor is a 4700uf 35v and appears to be in good shape, at least visually. That being said I am not sure if it is the faulty transformer or the capacitor or maybe something else. I did not have a multimeter that could verify a capacitance so I went ahead and ordered a BM867 from tme.eu and it should be here Monday. It appears that I have to remove a capacitor before I can actually test it according to this video: . What is the best way to discharge a capacitor while it is still soldered? Would me measuring the voltage across the capacitor leads be enough to drain it while it is still soldered?