Hello. I added a 3-wire Nexus case fan, plugging it into my mobo's "sys fan" three-pin socket. When I power on the PC, the case fan spins for 3-seconds then stops (the HSFan keeps going). When I shutdown the PC, the case fan spins again (before everything goes off).

Is it just that the PC is cool enough, so the "sys fan" socket sends no power to the case fan?

My system seems incompatible with monitoring sw (e.g., SpeedFan), so I don't have hard data.
If I power the fan via the large 4-pin, it goes.
I've updated the bios.

Many thanks.

We really need more information about your hardware before we can even guess at this. What motherboard?

The PC is an IBM A50p, P4 2.6. The motherboard is labelled "IBM Rev 2.1" (sorry - don't know how to get more details on the board). The HS is an XP-90, with a 92mm Nexus. Thanks again.

It is possible that the PC has a fan controller that stops the fan when it is not necessary. Unfortunatly, as we don't know what sensor it's using, or what the controls are, you kind of just have to take the results as they come. If you're up for some experamentation, you could play around with a hairdryer while the case is open and see if you can get the fan to start.

You might want to try installing MBM5 to get some data on temp (that is if your MB doesn't come with any monitoring software - but being IBM it must have something?).

Once you can get temp data, it might be easier trying to understand what's going on with your 'sys fan'.

Thank you for your replies.

While the PC is on, when I touch the fan, I can feel that it is getting power (a slight hum sensation).

And so I call IBM, and they ship me a fan to try out.
It is 80mm, 12v, 0.17a, SuperRed brand.
I unplug the Nexus (80mm, 12v, 0.15a), and plug in the SuperRed.

When I plug this OEM fan into the socket, it runs fine (that is, it runs when the PC is on).

Do you think I need to return this Nexus fan and get it replaced? Thank you again.

(ps - I have tried MBM and my board doesn't seem to want to play with it, so no data.)