The board has a special circuit that detects whether a 3-wire or 4-wire (PWM) fan is present. This circuit performs its detection at power-on (so don't plug fans in while board is (already) powered!). If a 4-wire (PWM) fan is detected, the fan will be powered constantly at 12V and the PWM signal (on the 4th wire) will tell the fan what duty cycle to operate at. If a 3-wire fan is detected, however, the circuit will instead vary the voltage of the power provided to the fan from 0 to 12V based upon the required duty cycle.
The fan detection circuit determines whether a 4-wire (PWM) fan is present by testing to see if a pull-up resistor is present on the PWM signal. If a 4-wire (PWM) fan is improperly detected, this is usually the result of the fan not having the pull-up resistor. Since the presence of this resistor is an absolute requirement (per the 4-wire PWM fan specification), fans that do not provide this resistor are considered non-compliant with the specification and will not be supported (i.e. all bets are off).
In the almost 10 years since we designed this circuit, I have never seen it fail to properly detect a compliant 4-wire (PWM) fan. I have, however, seen fans whose pull-up resistor has been blown and I have also seen fans that fry the board's circuitry (typically by improperly returning a higher-than-supported voltage on the tachometer signal - which is a good trick!).
Hope this explains things fully,
Thank you for this helpful information :-)
It explaned very well the 3-pin / 4-pin detection procedures of a Mainboard.
Didn't read this elsewhere in this clarity and simplicity, before.
Googled for pull-up resistor/logics issues with "Be quiet! Silent Wings 3 / 120 mm".
It seems they do not so well with at least some PWM Controllers.
"The situation is still unclear at this point, but what is clear is this: some PWM controllers
and the be quiet! Silent Wings 3 PWM fans do not get along very well. This can be remedied
if you are handy with electronics and electrical engineering, or simply know someone who does."
"The problem with the Silent Wings 3 series is that the controlling chip that they use has an internal pull-up logic
with 200K which is quite high. This results in a pretty low charging current of only 1.5µA (max) towards the aquaero (or any other fan controller).
There appears to be something to this claim, as Corsair Link Commander Mini and the PWM headers on the Gigabyte x99 Phoenix SLI motherboard
showed a similar fan control issue whereas those on the Asus x99 Rampage V Extreme did not.
It seems to be a mixed bag at this point so until it is cleared up my stance on the PWM versions remains unchanged.)"
Conclusions I'm taking out of it:
Since 4-pin plugs can hardly be plugged the wrong way onto a Mainboard,
and the 4-pin Silent Wing 3 Fan is plugged correctly, I see three possible scenarios left for me:
1. The Fan's (Silent Wing 3) pull-up resistor electronics is indeed broken.
(There's nothing I can do, other than a replacement.)
2. The Fan's electronics isn't broken, but it's not compatible with the PWM-Controller of this Board.
(There's nothing I can do, other than trying another Vendor's Fan.)
3. The Fan isn't compatible now, but I should absolutely update Board's BIOS to latest version -- to get it compatible.
(This measure should be tried before any Fan replacing.)
Can you please briefly comment on what is the most obvious step I should take, at this point?
Thank you again!
Well, based upon these other conversations, I would conclude that these fans are just not compliant with the 4-wir PWM fan specification. I would return them and look for replacements. If you cannot find other 4-wire PWM chassis fans to replace them with, just get 3-wire fans. The circuit also implements a voltage offset feature so that the response of 3-wire fans is similar to that of 4-wire PWM fans. While this feature was implemented to allow 4-wire and 3-wire fans to be used together, it also helps with the linearity of duty cycle response.
Your answers brought much light in a strange case, driving me almost sick. Thank you so much!
Glad you didn't recommend BIOS-Update as a solution, since I haven't UPS power environment for doing it securely.
Will keep the 3-pins alternative in mind and will seek for a fan replacement, the one or the other way.