Question Noctua Fans Intermittent Stalls. Fans do not spin.

[erosion139]

I have never seen this issue posted before, as all of them point to my fan speed profile not being of high enough power or my fan headers are not PWM based. Well, these are entirely irrelevant problems as the issue happens intermittently upon startup of the machine, (ex: Start PC, fan will not spin for the rest of the machines on time.) And the only way to fix the problem is to either go back and reboot it or unplug the fan and plug it back in. The fan control software will not help in this case even if I say set the voltage or PWM control all the way down and back up, so clearly, something is either wrong with that or the fan. At least you would think, until I discovered by checking the voltages on the fan header directly, (12V) how can this be possible? The fan is receiving 12V and not spinning a bit, and the PWM control is set all the way high. And if you are wondering, "well the PWM control must not be working" not true, I created an adapter that cuts the signal and RPM signal wires and only passes the positive 12V and ground wires to the fan, yet this problem still exists. It is looking an awful lot like the noctua fans (NF-A12X25) are faulty somehow. I have two of them and they both have this exact issue, the rest of my fans never do this and are from Arctic and I have used many other fans and never had a problem like this. So I have no clue what is wrong and it baffles me that this can be a problem for two units both costing 30$ each, it leaves a bad taste in my mouth for sure. I suppose I have to get them sent back? What a hassle.

Video I caught the fan not spinning and decided to capture the findings and odd behavior.

 

[Karadjgne]

Pwm is a modulated pulse. Out of the 4 wires one is ground, one is tach, one is a constant 12v. The last is the pwm signal wire. That signal pulses on/off and for basic intents and purposes it acts as the signal across a relay, stopping and starting the constant 12v flow into the fan. All that happens inside the fan, so it's not something you can change externally unless you interrupt the pwm signal wire.

That wire operates at 0.8v to 5.25v and requires 40mA. Feed it 12v and you'll more than likely burn out the resistors that make up the pwm circuitry.

Before blaming the fan, I'd do 2 things. Update any and all motherboard chipset drivers, USB and pci etc that are at the motherboard support website and verify the pwm signal voltage at the header. The fan must have at least 0.8v (constant at 100% duty cycle) on that signal to operate the fan, or the fan doesn't spin. Also has to have roughly a 40mA draw.

I have the same A12x25 (x2) and A12x15 (x2) on my rads, and all 4 work beautifully.

 

[Mr.Spock]

can you set the headers to run in DC mode and see if the problem persists?

 

[erosion139]

Pwm is a modulated pulse. Out of the 4 wires one is ground, one is tach, one is a constant 12v. The last is the pwm signal wire. That signal pulses on/off and for basic intents and purposes it acts as the signal across a relay, stopping and starting the constant 12v flow into the fan. All that happens inside the fan, so it's not something you can change externally unless you interrupt the pwm signal wire.

That wire operates at 0.8v to 5.25v and requires 40mA. Feed it 12v and you'll more than likely burn out the resistors that make up the pwm circuitry.

Before blaming the fan, I'd do 2 things. Update any and all motherboard chipset drivers, USB and pci etc that are at the motherboard support website and verify the pwm signal voltage at the header. The fan must have at least 0.8v (constant at 100% duty cycle) on that signal to operate the fan, or the fan doesn't spin. Also has to have roughly a 40mA draw.

I have the same A12x25 (x2) and A12x15 (x2) on my rads, and all 4 work beautifully.

So then my test before of running the fans through an adapter with the PWM lines cut should make the fan never spin, but the fan spins at 100% as if it were controlled using DC. Yet I still catch them doing the same thing. So is the PWM required or not? Maybe it is smart and knows how to switch between the different modes and perhaps my motherboard is killing the PWM signal or something. But I can tell you that you can definitely run these fans on DC only.

 

[erosion139]

can you set the headers to run in DC mode and see if the problem persists?

I have tried this through both a physical hardware connector and using the motherboard settings to control them with DC. I still catch them stalling however I think it is rarer.