Annoying fan speed problem

  • Thread starter Thread starter Peter
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Peter

Hi

I have an AMD64/ASUS K8N-E deluxe based system with a non-AMD cpu fan
(and hence slower, quiter fan). I have problems with the BIOS shutting
down the system shortly after a cold reboot.

Turns out that the BIOS is hardcoded to belive that any fan speed below
1800 rpm means there is a problem. My new fan runs at 1200 rpm at boot
time, which makes the BIOS shut down the system after a few minutes.
OK, some months ago I "fixed" that (with good help from people in this
NG) by disabling the fan speed monitor in the BIOS. This *used* to work
OK, until recently when - for no apparent reason - the BIOS seems to
belive that either the "Ingnore fan speed" option in itself or the 1300
rpms of the fan is again good reason to shut down the system.

My options seems to be:
1. Use the standard AMD supplied fan
2. Change the MB
3. Somehow make the MB belive the fan runs at a higher speed that it
really does...
4. Accept a number of shutdowns/reboots ...

I like alternative 3 best. Does anyone know how a fan reports it's
speed to the MB? Would it just report the voltage across the fan? Or
somehow the actual fan frequency/rpm? Or... ?

Thanks
 
Peter said:
Hi

I have an AMD64/ASUS K8N-E deluxe based system with a non-AMD cpu fan
(and hence slower, quiter fan). I have problems with the BIOS shutting
down the system shortly after a cold reboot.

Turns out that the BIOS is hardcoded to belive that any fan speed below
1800 rpm means there is a problem. My new fan runs at 1200 rpm at boot
time, which makes the BIOS shut down the system after a few minutes.
OK, some months ago I "fixed" that (with good help from people in this
NG) by disabling the fan speed monitor in the BIOS. This *used* to work
OK, until recently when - for no apparent reason - the BIOS seems to
belive that either the "Ingnore fan speed" option in itself or the 1300
rpms of the fan is again good reason to shut down the system.

My options seems to be:
1. Use the standard AMD supplied fan
2. Change the MB
3. Somehow make the MB belive the fan runs at a higher speed that it
really does...
4. Accept a number of shutdowns/reboots ...

I like alternative 3 best. Does anyone know how a fan reports it's
speed to the MB? Would it just report the voltage across the fan? Or
somehow the actual fan frequency/rpm? Or... ?

Thanks
Click to expand...


Hi,

I don't have an answer for your problem, but I think fan speed is
typically reported to the MB via a 3rd wire from the fan, which has a
"pulse" or "clock" type output as the fan spins, so it's not just a voltage.

Jim
 
OK, thanks; that would mean I would need to have a device - on that
wire - that could double that clock speed. Hmm, need to think about
that one.

Many thanks!
 
OK, thanks; that would mean I would need to have a device - on that
wire - that could double that clock speed. Hmm, need to think about
that one.
Click to expand...

If you think the fan is good, swap cpu and system fan connections.
 
Peter said:
OK, thanks; that would mean I would need to have a device - on that
wire - that could double that clock speed. Hmm, need to think about
that one.
Click to expand...

A crude (mechanical) device could be made from a dummy fan with the blades
removed - it would spin fast enough to satisfy the board, but wouldn't make
(hardly any) noise. A more elegant approach could be made from something
like a 555 timer in astable mode (depending upon the voltages required by
the tach sensor, of course).

Jon
 
Jon said:
A crude (mechanical) device could be made from a dummy fan with the blades
removed - it would spin fast enough to satisfy the board, but wouldn't make
(hardly any) noise. A more elegant approach could be made from something
like a 555 timer in astable mode (depending upon the voltages required by
the tach sensor, of course).

Jon
Click to expand...

Many thanks!
 
Jon said:
A crude (mechanical) device could be made from a dummy fan with the blades
removed - it would spin fast enough to satisfy the board, but wouldn't make
(hardly any) noise. A more elegant approach could be made from something
like a 555 timer in astable mode (depending upon the voltages required by
the tach sensor, of course).

Jon
Click to expand...

What I did was to take an old 80mm fan and cut off the blades; then
connected it to the CPU fan connector on the MB while connecting the
"real" CPU fan to a 12V connector directly from the PSU. Works just
fine, and hardly any noice from the dummy fan. Thanks!
 
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