Case fans running ALL the time?

Darkstrike · 05 Mar 2020

Hey all - I have a bit of an odd issue. Just finished building a PC for a young guy. His mobo died, so we ordered a replacement - all his other parts are being re-used.

The odd issue is that the chassis fans spin ALL the time, even if the system is shut-down? Even if the system is off, as long as the power switch on the back of the PSU is set to 'on', the fans spin constantly at seemingly a few hundred RPM (like...200RPM, maybe?)

Once the system is turned on, they spool up to their usual 'low temp idle' speed of like...500rpm...and work perfectly fine. The whole system, in fact seems to work perfectly fine except for this one weird niggle.

One fan is connected directly to the motherboard (a brand new ASUS B85M-G) and two of the case fans are connected directly to the PSU via molex adapters. The power supply is an older Thermaltake TR2 600w.

The CPU fan and video card fan do NOT spin unless the system is actually powered up and running. Not sure if the fan in the PSU spins when the system is off and the PSU switch is on or not - will check that after and report back as the system is in the middle of a Win10 upgrade at the moment.

I've never seen this before - is there a reason this may be happening? Thanks!

sygnus21 · 05 Mar 2020

That is weird... and the fans should at least shutdown when power is removed or the PC is off. Was this an issue with the previous board before it died?

Darkstrike · 05 Mar 2020

I don't think so, but I am not sure....at least if it was, he never mentioned it to me!

Come to think of it - I had removed the PSU separately and plugged it in to one of those "plugs into a PSU's ATX port to make it think it's hooked up to a mobo so you can use it as a bench power supply" adapters. This was while I was initially testing to see if the PSU or the mobo was the culprit. I wanted to see if I could get the PSU to power up separately as that would tell me if the PSU was dead or not.

I seem to think it MIGHT have done it when I was doing that, though I pretty much plugged it in and immediately turned it on the second after it was plugged in to an outlet...I'd turned it on so quickly I had one of those split second thoughts of 'hey, did those start before the PSU was turned on?" but thought nothing of it as I was pretty tired that day and thought I might just have been a little loopy...

Does this mean maybe I should get a different PSU for it? Is it possible there is something odd in the PSU that is going to murder this mobo as well?

sygnus21 · 05 Mar 2020

Well it would help to know that.

Also what What fans? And how many fans in all doing this? I count 3 - two to the board one to a molex cable.

With that, I "Could" understand the molex cable (though power should be cut there when the system powers down), but the board fans should definitely shutdown with a system shutdown.

That said, is there a setting in the BIOS for any type of fan control to include power settings?

sygnus21 · 05 Mar 2020

Darkstrike said:

Does this mean maybe I should get a different PSU for it? Is it possible there is something odd in the PSU that is going to murder this mobo as well?

I'd double-check the connections including the case's start / reset wires to make sure things were properly connected. You might also check that you left no pins or test switches connected to the PS. I doubt it's power supply at this time since everything else appears to be working fine.

Darkstrike · 05 Mar 2020

sygnus21 said:

Well it would help to know that.

Also what What fans? And how many fans in all doing this? I count 3 - two to the board one to a molex cable.

With that, I "Could" understand the molex cable (though power should be cut there when the system powers down), but the board fans should definitely shutdown with a system shutdown.

That said, is there a setting in the BIOS for any type of fan control to include power settings?

Nothing extra connected and all plugs are plugged correctly and as they should be - I triple-checked it all before I buttoned up the case as it's a bit of a cramped case to work in and I wanted to make sure all was well so I wouldn't have to take anything back apart again. As for BIOS settings, I went in and glanced and didn't see anything obvious unless I missed it...no weird controls there about fans or power supply that I could see.

As for the fans, I mentioned which were doing it in my first post, i.e. the chassis fans - two on molex to the PSU, one connected to a fan port on the mobo. The CPU and video card fans do NOT act oddly and shut off when the system is powered down.

- - - Updated - - -

***Just an update - the Windows updates finished, so I shut down the PC and the PSU fan does, indeed ALSO spin when the system is powered off, but the PSU's power switch is flipped 'on' as well as those three case fans.

Here is a screenshot of the voltages on the PSU...anything look out of the ordinary?

Case fans running ALL the time?-20200305_202450.jpg

sygnus21 · 05 Mar 2020

Well without seeing the system I've no further suggestions at the moment.

Just out of curiosity (and I have to ask) you don't have any of the fans coming off the CPU fan header do you?

Darkstrike · 05 Mar 2020

sygnus21 said:

Just out of curiosity (and I have to ask) you don't have any of the fans coming off the CPU fan header do you?

Just the CPU fan! :P

sygnus21 · 05 Mar 2020

OK, try this (may or may not work)... going by the owner's manual for the board on page 1-11 there's a Keyboard and USB Jumper switch. Move the jumper switch to the +5VSB position. If there move the other way and see what happens after a reboot and restart.

In other words do a system shutdown then boot up and after things settle do a restart. Are fans fixed?

The other thing you might look at is proper grounding and setup of the motherboard in the case - are all the standoff there? Are there clear grounding scorch marks showing?

rvcjew · 06 Mar 2020

sygnus21 said:

OK, try this (may or may not work)... going by the owner's manual for the board on page 1-11 there's a Keyboard and USB Jumper switch. Move the jumper switch to the +5VSB position. If there move the other way and see what happens after a reboot and restart.

In other words do a system shutdown then boot up and after things settle do a restart. Are fans fixed?

The other thing you might look at is proper grounding and setup of the motherboard in the case - are all the standoff there? Are there clear grounding scorch marks showing?

I was thinking this, shorting in the case for a like a ground loop type situation. I would build the system out of the case and test it. Also perhaps the psu is messed up in its pins internally. You said you used a jumper to make the psu run out side the case but did you ever try running the psu with it unplugged without the jumper?