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Noctua CPU fans not spinning up


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Update: The fans now spin up after removal of the low noise adapter cables. The fans work as expected when they are connected directly to the CPU fan header via the supplied straight-through "Y" adapter cable.


The basic problem is now circumvented but I am curious about the effect. Why would the HX1000W not power up these fans through these adapters when a 600-Watt PSU from another mfr will?


Original post:

I use the Noctua NH-U12P CPU fan kit which uses two NF P12 fans. They are connected through the supplied "Y" cable to three of four pins on the CPU fan header on the M4A79T.


When I upgraded the power supply, the fans stopped spinning up and the BIOS now reports a "CPU Fan Error" message. The fans move very slightly in the expected direction twice during startup but they will not keep going unless I give them a push manually, after which they keep running. So, they are receiving power, but not enough for fan startup.


The fans worked fine with the previous 600W PSU (from a different manufacturer) even though 600W is the minimum recommended for this MB. I upgraded to the HX1000W mainly because I wanted quiet, which I now have.


I have checked the connections to the fans, played with BIOS fan settings, turned off the case fan near the Noctuas, and tried different combinations of the 8-pin PSU-MB connector nearby (one 4-pin, the other 4-pin, and the 8-pin). No changes result.


The PSU selector on this site includes the HX650W in the recommended units, so I trust that the HX1000W should work, too.

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From Noctua support:


To be honest this seems quite odd, since we have a similiar mainboard (M4A78T-E) in

our testlab and I just did some tests with different power supplies (including a

Corsair TX750). With none of them did I experience the problems you describe and

since it worked before I'm pretty sure it must have something to do with the power



The ULN-adaptor is just reducing the input voltage to the fans, so if you have

reduced voltage on the resistor inlet, the output voltage will be even lower. You are

using two adaptors for the two fans, correct?


I believe the reason could be that the 12V rail going to the mainboard gives out a

lower voltage than the other PSU. We have one PSU with 11,9V and I even tested it

with a non-PC PSU at 11,7V and the fans started as intended.

But if the PSU is really supplying 11,7V and less to the mainboard, there is probably

something wrong with it, unless you have extremely powerful components installed that

would max out the PSU.



Best regards,


Noctua technical support

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Is there any way to get the retailer, NCIX, to do the swap? For one thing that would save me $35 in shipping costs. I am also concerned that this may be a design or compatibility issue and the RMA may be a waste of time and money. If the power supply were dead I am sure NCIX would replace it but since this is a somewhat esoteric problem, I think a note from Corsair would be helpful.


In the last few months I have bought several Corsair products: four sticks (2 packages) of DDR3 RAM, two 64 GB Extreme SSD's and one HX1000W. One of the SSD's failed (dead) after about a month, and now the power supply appears to have a problem. That's a 40% failure/problem rate.

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Ram Guy,


Thanks for the offer to replace this unit. I don't want to send it in, however, unless Corsair has confirmed that this model should fire up the CPU fans. Thirty-five dollars is too much for me to spend if Corsair is only guessing.


The retailer, NCIX in Burnaby, BC, was kind enough to try another unit, brand new from the box, with the same results. So, either both units are defective or this is a design and/or compatibility issue. My guess is the latter.


The fans work without the low-noise adapters. This also allows me to use the BIOS settings for the CPU fans, so they run as low as 700 rpm, removing the need for the adapters.

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