[Tfug] m board

[arizray at comcast.net]

Thanks. No, the new fan is neither spinning or running. Yes the fan has three wires, red, black and white. You described finding +12v at the yellow wire. Wouldn't the 12v be across the red and black instead? 
 -------------- Original message ----------------------
From: Bexley Hall <bexley401 at yahoo.com>
> --- arizray at comcast.net wrote:
> 
> > Actually I ordered and installed a new fan. The
> > presence of the fan is just not being detected by
> > BIOS. I does not run at all.
> 
> Your answer is vague.  So, I'll repeat my question:
> 
> Is the {old,new} fan spinning?  (obviously, this is
> a key issue in getting the right diagnosis)
> 
> There are only a few different ways for a device to
> tell if a fan is operating (i.e. spinning) -- one
> assumes the MoBo is not just interested in whether
> or not the fan is *attached* but whether or not it
> is actually *spinning*!
> 
> Most commonly, this is done witha three-wire fan.
> In addition to the two power leads (red & black,
> most often), there is a "sense" lead (yellow)
> that delivers pulses from a hall effect sensor
> in the fan.  These pulses are generated by the
> rotating motion of the fans blades.  I.e., you can
> tell if a fan is *operating* and how fast it is
> spinning (presumably, you can infer from the
> fact that a fan is "spinning" that it is "connected"!)
> 
> Assuming your (new!) fan has all three wires (and
> is plugged into the CORRECT CONNECTOR), if it is
> not spinning it is a power problem.
> 
> Older MoBo's just supplied +12V to the fan and
> watched to see how fast it would spin (if they
> even bothered to do *that*!).  On such a system,
> if +12 was absent, then the fan wouldn't run.
> 
> You can check +12V at any of the disk drives
> (yellow wire).  If it is not present, then you've
> most likely got a blown power supply.
> 
> Newer MoBo's control the speed of the fan.  Since
> it is a DC fan, speed is controlled by varying the
> voltage across the fan.  The system can then
> increase or decrease the fan's speed to better
> balance heat/noise issues.  In theory, the system
> can drive the control to get a specific fan
> speed (e.g., 1200 RPM) from the fan by implementing
> a closed loop control system (i.e., look at fan's
> speed; if less than what you want it to be, increase
> voltage to the fan; else decrease; lather, rinse,
> repeat)
> 
> Since you have enough of the system running to get
> the processor talking, the power supply isn't
> *completely* dead (IIRC, most PC switchers regulate
> off the +5V and let the +12 et al. follow...?)
> 
> --don
> --don
> 
> 
>       
> 
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