14.02.2021 13:13

Fixing the APC Back-UPS CS 650EI random beeps

For several month the UPS randomly beeped - usually those were two short beeps several times in a row. It was not easy to find what was going on as I am not sitting right beside the UPS, but during silent nights the beeps were heard clearly. Once working on the server I was lucky to see this happened and during that time the red battery warning light comes on. I've bought a new battery in a good fate this will fix the annoying beeps. Well those were wasted money as the reason is - again -  the bad capacitor.

Replacing the C26

Opening the UPS is quite simple just by removing two screws at back, then the plastic parts fall off. There is a 470uF/16V capacitor C26 right next to the soldered 40A fuses on the main UPS board. I would not consider this exactly a design flaw as the UPS is more than 10 years old. However this place is receiving a significant heat (you see the heat sinks nearby), therefore the capacitor lost his capacitance and was causing a random detections of bad battery.

Replacing the capacitor is quite strait forward... no more beeping.

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