Power supply dying?

[Tasiin]

Well, this is an interesting problem. For the past couple of days, I've noticed that one of my case fans has been slowing down and speeding up at odd times, and it's been slowly getting worse every day.

At first, thinking that my motherboard might be somehow adjusting the fan speeds, I tried a similar fan that hooked directly into the power supply instead of the motherboard, which should prevent that happening. Same problem. I then tried a third fan, and it too had the same problem.

After trying that, I went into the BIOS and took a look at the fan speed. When the case fan begins to audibly slow down, the speed drops to 2840 RPM from around 3013, which is the correct speed for my fan. It's not a huge drop, but it does seem to be having a very adverse effect on the temperature of my video card and chipset, and hearing it slow down and speed up every fifteen seconds or so is getting annoying.

The only possible thing I could think of that could be causing this is the power supply. Is it possible that it is somehow not providing stable power to the fan, and the speed drops whenever there's a dip in the current? The power supply is an Antec NeoPower 480, and it's currently powering an X2 4400+, 7800 GTX, one DVD drive, a 36GB Raptor hard drive, 1GB of memory, and a DFI NF4-D motherboard. The power supply is probably not even six months old, and I bought it shortly before upgrading my old system with the components you see above, so I'm a little confused as to why it'd be having problems already.

If anyone has any ideas on this, I'd really appreciate it. I've seen a lot of strange stuff, but this is definitely odd, and I'm at something of a loss at the moment. Thanks!

 

[meltdown75]

Hi there.

Check to make sure you don't have options enabled in BIOS which control the system fan speeds when certain temperatures are reached. If I recall correctly, Asus has something called QFan which throttles the fan speeds based on your specified settings, so I wouldn't be too surprised if other mobo manufacturers had the same type of software / options in BIOS.

I usually turn my fan control off because, like you, I like my fans to be running at a stable speed and not dipping. I like them to be at max speed at all times.

Your PSU is another issue. I doubt that the very small amount of power drawn from a CPU fan could affect the overall stability of the PSU, whether it was functioning at 100% or not.

One way to check the integrity of your PSU is to monitor the voltage ratings on the respective rails while the system is in use. You have a +12V, a +5V and a +3.3V rail. If the voltage reading on any of the rails is 5% higher or lower than the specified voltage, you may be having problems and might want to try another PSU.

For example, if you check the +12V rail and you see it is reading at 11.35, you definitely have issues.

All that said, I'm no PSU expert... just getting discussion going. Hopefully some of my blathering helped Good luck

 

[Tasiin]

Yeah, I did check that, and made sure that was all disabled. I also used a fan that used a 4-pin molex connector rather than the 3-pin one that hooks into the motherboard, so there's no way the motherboard can control that. There was still a noticeable variance in fan speeds with that, which should not be happening.

Also, if this helps, I found an old screenshot I took a week or so ago of MBM 5 back when everything was working properly, and I took a screenshot of it now for comparison.

Working properly: http://img355.imageshack.us/img355/9481/old2qv.jpg

Slow fan: http://img239.imageshack.us/img239/9715/new8vq.jpg

The "80 Exhaust" speed is the fan that seems to be having problems. You can also see the power supply's rails in those pictures, which was something you suggested checking. I know checking that sort of thing from software isn't as accurate as taking something like a voltmeter to it, but I unfortunately don't own one of those, or know how to operate it. The rails seem fine to me though, if they're accurate. Not perfect, but it's always been around that.

Thanks for your help!