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"Broken" be quiet! PSU fan may be an easy fix (sort of)


Major Contributor
Nov 6, 2018
Story time:

My office PC had been graced by a Fortron FSP350-60APN power supply since 2012, which started to develop a noisy fan a while back that I was unable to fix entirely, presumably because I had not removed the little retaining washer / clip when trying to oil the fan bearing (see Mr. Carlson's Lab video). The fan ran fine with the machine laying on its side, but that's not entirely elegant. The old supply also was single voltage input and plain 80PLUS rated only.

So along with a general fan upgrade (Noctua NF-A9 PWM for the EKL CPU cooler + be quiet Pure Wings 2 92mm for exhaust), I decided to splurge on a semi-fancy PSU, a be quiet! Pure Power 11 400 W. (I would have preferred a used Straight Power 10 as their fans are reportedly even quieter and parts quality should be higher in general, but eBay is currently off limits to me as their payment options and mine do not overlap.) It current is the least expensive, lowest power 80PLUS Gold rated PSU you can get around here.

After installation and wrestling with the cables (this old mid-2000s Asus minitower case is a bit tight, but I still liked it better than the newer very lightweight one the system came in originally), I was greeted by a non-running PSU fan. Once gently bumped with a screwdriver, it slowly set in motion with a clear tick-tick-tick sound, as if the fan blades were hitting something. Well sh**. :facepalm: So much for their QC these days. Someone may have wanted to make up for production downtime during the pandemic.

Now this system draws about 18 W from the wall in idle and at most 59 W fully loaded, so you could probably run the PSU fanless just fine, plus it was late by the time I was finished, so I left it at that.

Yes, I could have ripped the PSU back out, boxed it up and sent it back. I did, however, want to know what the prroblem was, and see whether I couldn't fix it myself. With the problem occurring out of the box and irrespective of orientation, there had to be some sort of assembly error. Was it the fan itself? Or perhaps an external obstruction?

The top case can be removed after undoing 5 small screws, 4 on top and one on the side under the (not actually legally binding) "warranty void" label. Removing the fan plus external grille then takes another 4 bigger screws. Take note of the fan cable routing. The fan seemed to be plugged in via a tiny 2-pin connector but the cable was really wedged in there, so I did not bother to unplug it.

Spinning the fan by hand revealed quite a bit of noise. Under the label, I found plastic (possibly a plug) where a sleeve bearing fan would normally have a rubber plug. Hmm. I decided to test for incomplete assembly by giving the fan hub a good push, and with a click the rotor proceeded to seat in place. And what do you know, we've got a smoothly turning fan. :D

Reassembling a PSU always is a bit finicky, ideally you'd have three hands but two will do in a pinch, too. Don't make the stupid mistake of mounting the fan in reverse (ask me how I know...). Make sure the case goes back together properly, slotting in as required. This wasn't my first power supply but the metal seems to have gotten rather flimsier at least in this class, which can be both a pro and a con.

Once operating properly, the fan has a minimal amount of pole noise... so the motor driver is not exactly Noctua grade. I knew that from my Straight Power 11. It's still very quiet though. Since the case is partially damped with bitumen mat, vibration is not being amplified to a problematic degree. While in theory you may be able to use rubber nipples for fan mounting, I have my doubts about whether those would provide enough pressure to keep the grille attached firmly enough for shielding to be effective.

If I were be quiet!, I'd be making a special tool that permits giving the fan hub a good push straight down through the grille - a piece of wood with carved slots at the appropriate distance would probably do. This would permit fixing any RMA'd PSUs affected by this particular issue within seconds.
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