Preventing a PS fan going high-speed / noisy in an HP DX6120

[Apprentice_GM]

Hi everyone (first post)

First, many thanks for such a wealth of information provided in articles and on these forums. I have been lurking and reading (nearly) everything for the last few weeks, and it's been terrific to see so many low/no cost solutions using common materials to the silent + cool issues cropping up. My particular favourites are the elastic suspensions of HDD's!

I have been undervolting fans with resistors and struggling with adequate airflow volumes on my own for ages, you guys have clearly identified when it's best just to buy a different component and which one (using the recommended lists) is preferred under which conditions - so thanks a lot to all those people making so many valuable contributions here.

I have a problem which I can't find a solution using SPCR forums search or Google and was hoping for some advice.

I have a pretty quiet HP DX6120 (mini desktop) that for the last few weeks has been constantly switching the power supply fan (a Delta AUB0812VH) from a very quiet low speed mode into very high speed mode, which is ridiculously noisy. The PC has a 92mm front intake fan and a 70mm PU heatsink extraction fan as well. When PS fan is in "normal" low-speed mode the total noise from the case is ~28 dba I am guessing, which in this office environment of >30 dba is inaudible to me even though it sits in front of my keyboard (<1m from my ears for sure).

However when the fan goes into high-speed mode it is around mid to high 50's dba I am guessing, and certainly incredibly annoying and grating on my nerves.

The PS fan is plugged into the PS Circuit Board with a 4-way pin connector (Yellow/Blue/Red/Black). There is no BIOS setting for the PS fan, and nor is the PS connected to the mobo via a data cable anyway (obviously it is connected via power cables but afaik they don't carry any data eg fan speed data or temp data).

So I am guessing either a temp sensor in the PS unit is mal-functioning and causing the PS to tell the fan to switch to high-speed/noisy mode, or whatever "smarts" might exist aren't being smart (have failed). If I give the PS a thump it will slow down / quieten down again for a while.

If I feel the air blowing out of the PS it is cool, even in low-speed mode, so I doubt any temp is high enough anywhere to warrant such behaviour.

If I take the case off and leave it off, the PS behaves all day, not going into high-speed / noisy mode even once.

I can't believe the case lid causes greatly increased temps inside the PS (as above the air is quite cool when PS fan in low speed mode with case lid on), however, leaving it off definitely stops the noise, the PS fan spins away quietly and happily all day.

I am trying to work out if the case lid force the PS into a position that would restrict airflow, but as far as I can see it has no bearing - the PS has vent holes all around it and they aren't blocked with or without the case lid on.

The PS itself may just be faulty, but I wouldn't know what to check.

Does anyone have any ideas or suggestions? Thanks in advance!

[MikeC]

These customized proprietary functions are often the worst to deal with. Studying any documentation -- maybe tech manuals from HP -- might help shed light on how the thing works -- or is supposed to work. That a thump slows the fan down is not a good sign at all.

A 4-wire pin suggests PWM control. 2 of the wires carry voltage, one caries the RPM signal, and one carries the PWM freq signal. You might try unplugging this connector from the motherboard while the system is idling and see what happens. If the PSU fan stops but the system keeps running, then you're home free -- just plug a Zalman fanmate into the MB header (there will be only one way for it to fit) and plug the fan connector from the PSU to the Zalman output. Again, there is only one way it will fit.

I suspect it will be more complex than this though.

[Apprentice_GM]

I had the power supply replaced under warranty. All has been well for over a week - blissful peace and quiet at last.

I forgot to mention before it was my office PC doing that, I reckon that particular HP model was pretty well designed for a normal office ambient noise level it was "noiseless" - less than say 28 to 30db office environment?

Anyway, just in case others have the problem I had - because it was the PS "smarts" cutting the fan in too hard and too early the only solution (unless you are really low-level electronics technical and I'm not) is to replace the PS.

Now off to silence my home PC . . .