[Tfug] m board

[arizray at comcast.net]

You are correct and were clear.
 -------------- Original message ----------------------
From: Bexley Hall <bexley401 at yahoo.com>
> --- 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
> > > 
> > > 
> > >       
> > > 
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> 
> 
> 
>       
> 
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