Motherboard Problem

[JSmr]

Ok, here's the deal. I will try to describe my problem as thoroughly as possible. I have recently bought 3x ASUS M2N-SLI Deluxe Motherboards. They work great. I do have one small problem that I have encountered though. My case has a rear 120mm fan. When I plug this fan into the MB into any of the recommended Chassis Fan slots it will not run when the computer is in operation. I have found though, that if I unplug the fan and plug it back in while the computer is running it will begin to spin and continue to do so until the PC is turned off. I have searched the BIOS but to no avail. If anyone could help is would be greatly appreciated.

Thanks in advance,
JSmr

[Thrax]

Can you check your BIOS and report the 5v, 3.3v and 12v voltages to us?

[JSmr]

Sure can.
3.3v -> 3.33v
5v -> 5.10v
12v -> 12.24v
Vcore -> 1.36v

[JSmr]

I have also noticed that if I unplug it and plug it back in while it's running, the BIOS recognizes it and begins to monitor its speed. But when the computer is just booted, the Fan speed is 0

[Thrax]

Are there any BIOS updates available for the motherboard? Is the fan particularly high-RPM?

[JSmr]

No on both counts, the BIOS is the newest one, and the fan is just a plain 120mm factory standard

[Thrax]

How about an 80mm fan? Does that work properly?

[JSmr]

I don't have one on me that I can try.

[Thrax]

Let me give you my prevailing suspicion:

120MM fans are fairly power-hungry, particularly when you consider the 3-pin connectors on a motherboard which are usually starved for power. I'm suspecting that the circuits designated to these connectors aren't receiving enough power at boot (When there's a large spike in power required elsewhere on a mobo), but is providing enough voltage once the flow is nice and regular.

It's the difference between a human having 120 gallons of water dumped on him in two seconds, and drizzled on him gently over the course of an hour. Same amount of water (voltage), but obviously one is easier to take.

[JSmr]

hmm I understand, well what do u think would be the solution?

[Thrax]

It's hard to say what the solution is without having a weaker fan, such as an 80mm or 60mm, to test with. If the fans came with a 3pin -> 4pin molex connector, which allows you to hook it directly to the PSU, trying hooking the fan up to that. If the fan powers on with the PC, you know that the connectors on the motherboard aren't sufficient for the fan you have.

[JSmr]

Allright, thanks a bunch ill look some more into it once I get access to my 80mm fans.