[Tfug] m board

[Bexley Hall]

--- 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