Forgot to say that I have tried to connect fan and adapter to the board while running and the fan starts normally -- it is only at cold boot that I have this issue with fans not starting so it might really be the BIOS and fan controller IC programming issue.
it seems the startup voltage is too low for this fan. you could try to trigger them using the controls of the desktop control center application.
Sorry, but I do not use DCC, nor I would like to use it manually each time I boot the system just to kick up the fans.
Furthermore, fan motors would have plenty of chance to burn out between the moment I power on the system, and the moment I start the DCC or if I forget to do it alltogether.
Finally, if I set fan control to OFF in BIOS I would expect it to work that way and provide full voltage at startup.
At least that is what I expect from a $250 high-end board made by Intel.
does the fan startup on the 4-pin fan-connector ?
I haven't tried it because there is only one of those available (not counting the CPU fan), and I need to connect two fans (front and rear).
Frankly, I do not understand what you are trying to prove? Please explain your idea.
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it provides a little more current. i am curious if it makes a difference.
Yes it does... it can start off the 4-pin connector but not off the 3-pin!
This board has:
1x CPU fan header (4-pin)
1x fan header (4-pin, back)
2x fan header (3-pin, front/back)
From aSC7621 datasheet typical application shows that PWM3 is shared between two fans. Could that be the case here?
Although I don't understand this:
If (vastly simplified formula) 1300 RPM : 12 V = 900 RPM : x V
Then with x = 8.3 V, and fan rated 1.08 W at 12 V:
1.08 W / 8.3 V = 0.13 A
0.13 A should not be such a big deal, right?
I simply can't, no, I refuse to believe that a $250 board can't power a simple high-quality silent fan!
well, the resistance is, with this fan, too high for the 3-pin. other fans may work fine on all connectors. I use all 3 with no problem. that's all i can add to the subject matter, sorry.
Then, how do you explain that the fan starts if connected to the board which is powered on?
It is only at cold boot that it cannot start on 3-pin, if you plug it while the board is running then it starts fine.
i was referring to the "startup condition". the "kick" it gets from the board starting fresh up is too weak. condition changes after startup. logical ?
Hmm... condition should not change.
If there is enough current/voltage later on, it should be enough at startup as well unless fan controller IC is not being programmed correctly by the BIOS.
This PWM IC has an option of controlling spinup time, that is why I am suspecting bad programming. I contacted support and escalated the issue, I am waiting for an email from them.
Have exactly the same problem here. It manifests itself with the high speed Noctua P12 fans. I have a number of S12 fans installed too and these seem to work fine with or without resistors. At the moment I have a P12 attached to the 3 pin rear header and if I use a resistor, it would require spinning up by hand as mentioned in the OP. Removing the resistor cures this issue although it does take a second or two to spin up. I did manage to get a second P12 running on the front fan header with the LNA resistor but again, spin up is delayed. I'm running two Akasa Apaches on my CPU cooler using a PWM splitter and these work fine, even though both fans are effectively drawing current through the CPU fan header. At the moment it means my rear exhaust fan has to be run at full speed all the time since Intel's Desktop Control Centre is incompatible with Win 7 and other than crippling the speed in the BIOS there is no other way to control the speed. It's not as big deal for me and I think the best interim solution will be to move both of the S12 fans off the motherboard and run them directly off the PSU.
Connecting P12 to rear 4-pin fan via resistor worked for me but I need to connect two of them (front and rear). Running of the power supply is simply unacceptable because you lose ability to monitor rpm and you add more cable clutter.
Igor, not suggesting that we should have to run off PSU but if you wish to adjust the fan speed down I don't see we have much choice but to run off PSU with resistor or perhaps install a fan controller. Clearly there is some issue with the P12 and the 3 pin headers on the motherboard. Personally I don't feel the need to measure the rpm. Noctua have stated the rpm speeds using the various resistors. Of course this is not as accurate as a direct reading but does this really matter? Cable clutter is an issue that is easily solved with a decent case or some cable ties. I'm not disagreeing with you here. I would like to see this motherboard have the ability to spin up a 12 cm fan but it struggles and I was merely suggesting an easy and inexpensive workaround.