[Tfug] m board

[Bexley Hall]

--- arizray at comcast.net wrote:

> 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? 

No, I said the yellow wire ON THE DISK DRIVES
is a convenient place to get at 12V.  I said the
yellow FAN wire is the "sense" wire.

(please reread my post -- I thought I was clear
on this)


>  -------------- 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
> > 
> > 
> >       
> > 
> > _______________________________________________
> > Tucson Free Unix Group - tfug at tfug.org
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> 
> 
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