I’m using Ubiquiti networking gear to provide wireless connectivity at home. I’m happy with the easy of installation, management and performance of the devices. In the last weeks I started to notice that the UAP-AC-PRO that is mounted at the ceiling in my office space started making a buzzing/whining noise. This was not the case when I first installed it quite some time ago.

After checking if other people are noticing the same issue (which some people do apparently) I wanted to silence the device again as it started to really annoy me while focussing to get work done. I tried different power supplies, different ethernet cables but none of that worked to restore the device to ‘silent mode’.

Spoiler alert: I got it fixed and it just takes 10 minutes of work if you know which parts to replace…

I opened the device based on these instructions. Just take your time. In my device there was a little glue/sticky material keeping the two halves tightly fixed together but with some perseverance you can open the snap locks of the enclosure without damaging it.

Then I started searching for the noise source on the PCB. The buzzing started about one minute after boot of the device, when the white LED that is on while booting goes out. As the buzzing sound is quite high pitched it is not really easy to determine the exact source. At first I suspected the big transformer for the PoE section of the device, but I could not silence the device completely by squeezing / pressing / fiddling with it. On to the other components on the board. It took me quite some time but I ended up locating the uP9617 DC/DC convertor that is located next to one of the antennes on the board as source of the whine. It has a magnetically shielded 3.3uH coil and an electrolytic capacitor (22 uF, 16V) that are part of the switching circuit. Either one of both, or both components are the likely noise source.

After checking the junkbox I found potential replacement parts. Replacing the inductor alone did not help. Replacing the capacitor alone did not help either. Replacing both the inductor and doubling the capacitor value to 44 uF by adding a second parallel capacitor removed the buzzing noise completely. I checked the output voltage of the convertor (needs to be 3V6) and the stability of the output voltage and all is working as it was with the original parts, except now they work silently.

The access point is mounted on the ceiling again. All is quiet again. Bliss!

References to replacement parts are:

• Inductor: Murata 1255AY-3R3N-P3
• Capacitor: 2 x MLCC X5R 22uF 16V