CPU fan not starting up on boot

[MRIM]

I just booted up a system I've built:

Antec P182, Gigabyte X48-DS4, Seasonic S12-550, 2 Noctua S12-1200 case fans and 1 Noctua P12 CPU fan on a Noctua NH-U12P heatsink

The two case fans are connected to the sys1 and sys2 fan headers on the motherboard (both 3-pin, no PWM), and the CPU fan is connected to the CPU fan header (again, 3-pin). I've ensured that they are connected properly and securely. The first time I booted up neither of the case fans was running but the CPU fan was. I then turned the computer off and reconnected all the fans to make sure they were secure with the headers. Now when I boot up the opposite happens: the case fans start but the CPU fan doesn't. The thing is, if I just touch one of the fan blades on the CPU fan it starts moving.

In the BIOS I turned off the Smart CPU fan feature, which was on by default. The other odd thing is that when all three fans are running and I go into the BIOS diagnostics screen, it shows the CPU fan RPM speed but both case fans (which I can clearly see are running) show 0 RPM. All three fans are using the ULNA speed adapters provided by Noctua. I haven't tried removing the adapters yet as I'm running Memtest right now. Any ideas?

 

[Injury]

Do you have a bunch of items "daisy-chained" on the same powerline? I've had that happen before and the fix was to break things up a bit.

The only other thing I can think of is that the speed controllers on your mobo are fudged.

 

[MRIM]

The PSU comes with I think 3 molex chains, none of which I'm using. There are two SATA power chains, each one having only one device connected to it. Both 6-pin PCI-E connectors are connected to a Radeon 4870. I'm using an 8-pin 12V connector for the motherboard per the suggestion of people on this forum (there's also a 4-pin connector available).

Ugh, I hope I don't have to RMA this motherboard.

 

[MRIM]

OK, so Memtest passed the first pass for all 8 gigs of RAM fine. Then I shutdown and removed the ULNA (ultra-low-noise adapter) from the CPU fan and replaced it with the LNA (low-noise adapter), and removed the LNA adapters from the case fans. Now all three fans spin on boot up and I can see the RPMs for the two case fans in the BIOS. So I guess it's a voltage issue since I believe the Noctua adapters use a resistor to lower the voltage of the fans? I've read about motherboards needing a certain level of voltage to start up fans before but I'm not very knowledgeable about the issue. Is this a known issue with the Noctua adapters?

 

[PianoMan]

You're exactly right about the resistors and why the fans weren't spinning. I was about to suggest removing the adapters, but found this thread too late.

Fans need a minimum voltage to start spinning, to overcome both mechanical and electrical inertia. Seems the ULNA adapters drop this voltage too far (since you've turned off the smart fan controller). I'd think Noctua would have designed for this, but aren't too familiar with their fans (but would like to be ).

Mebbe someone else can chime in?

 

[cubeless]

this happens when i use the bios fan speed control... if set to 'keep cpu @ 45c' with my vendetta2 the cpu starts up around 35c and the fan just sits there and kind of twitches until i start doing something to warm up the chip...