Author Topic: APC UPS Backup Repair Question  (Read 1348 times)

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Offline delfin2003Topic starter

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APC UPS Backup Repair Question
« on: March 16, 2017, 10:45:00 pm »
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?
 

Offline james_s

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Re: APC UPS Backup Repair Question
« Reply #1 on: March 17, 2017, 12:45:56 am »
Usually a capacitor and connected circuit will discharge itself within a few seconds of the device being turned off. This does not necessarily apply to HV circuits but in this case the cap is only 35V so just check the voltage across it.

Are you sure the capacitor is making the chirping sound? That would be rather unusual.
 

Offline delfin2003Topic starter

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Re: APC UPS Backup Repair Question
« Reply #2 on: March 17, 2017, 01:18:39 am »
James, I am pretty sure it's the capacitor that makes a very soft chirping sound but I am not 100% sure. I guess I will de-solder the cap sometime next week and check it. I don't think there is a better way to tell where the sound is coming from...I'll post an update as soon as I check the cap
 


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