Smart UPS 1000 - really bad buzzing sound

[Anonymous user]

I just bought an used Smart UPS 1000 and replaced the batteries with new ones. This UPS has a really annoying buzzing sound which doesn't stop after the batteries have been fully recharged. It goes on for like 10-15 seconds, stops for a second and then begins again, and the cycle repeats. Doesn't matter that the batteries are at 100% or that there is nothing connected to the UPS or that the UPS is off (not unplugged), the buzzing noise goes on for as long as the UPS is connected to AC or the batteries are not disconnected. It's not the big transformer buzz, because I have checked. If I unplug the batteries connector on the back side of the UPS, the frequency of the buzzing is reduced, but not the volume.

I tried to localize the noise and it's coming from the area between the 2 small transformers on the PCB on one side and the not so small inductors on the other side. In that spot is a big white box, but I have no clue what it does. I would gladly replace/fix it myself if I knew what it was.

Any advice is welcomed.

Thanks!

[Erasmus_apc]

Unfortunately we cannot provide part information for repairs of this nature, or support the replacement of internal UPS parts.

My advice would be to contact an out-of-warranty service center like Coastal Business Machines (http://www.cbmi.com/), or contact our sales team for a Trade-UPS.

[BillP · Accepted solution]

maybe KVar (another user here) can chime in.