Fooling motherboard into booting without CPU fan

Hi,
Is it possible to fool a motherboard into booting even without the
fan attached (assuming it checks the rotational speed before
proceeding)?
I thought shorting the 'SENSOR' and 'GROUND' pins would work at
first, but if it's being used to detect the fan speed, then maybe not?
The CPU_FAN connector on the Gigabyte motherboard has 3 pins
(SENSOR, 12V and GROUND), if that's relevant(?).
Any help would be appreciated, thanks!

- Michael Strorm

Michael Strorm wrote:
> Hi,
> Is it possible to fool a motherboard into booting even without the
> fan attached (assuming it checks the rotational speed before
> proceeding)?
> I thought shorting the 'SENSOR' and 'GROUND' pins would work at
> first, but if it's being used to detect the fan speed, then maybe not?
> The CPU_FAN connector on the Gigabyte motherboard has 3 pins
> (SENSOR, 12V and GROUND), if that's relevant(?).
> Any help would be appreciated, thanks!


You should be able to go into the BIOS and disable the CPU fan check. I
do this, as my CPU fan is 2-wire.


-WD

use a 1.5v battery between the 3rd pin and ground. My 4000RPM fans run
around 1.7 volts.on the tach side.

"Michael Strorm" <> wrote in message
news: om...
> Hi,
> Is it possible to fool a motherboard into booting even without the
> fan attached (assuming it checks the rotational speed before
> proceeding)?
> I thought shorting the 'SENSOR' and 'GROUND' pins would work at
> first, but if it's being used to detect the fan speed, then maybe not?
> The CPU_FAN connector on the Gigabyte motherboard has 3 pins
> (SENSOR, 12V and GROUND), if that's relevant(?).
> Any help would be appreciated, thanks!
>
> - Michael Strorm

On Mon, 06 Oct 2003 00:03:36 GMT, "jpsga" <> wrote:

>use a 1.5v battery between the 3rd pin and ground. My 4000RPM fans run
>around 1.7 volts.on the tach side.

That sounds like a bad idea, it is not a voltage level being detected
from the fan, it's the pulse rate.

Neither should the sense pin be grounded. The poster who mentioned a
bios setting to disable the fan error-stop was correct.


Dave

kony <> wrote in message news:<>. ..
> On Mon, 06 Oct 2003 00:03:36 GMT, "jpsga" <> wrote:
>
> >use a 1.5v battery between the 3rd pin and ground. My 4000RPM fans run
> >around 1.7 volts.on the tach side.
>
> That sounds like a bad idea, it is not a voltage level being detected
> from the fan, it's the pulse rate.

Yeah, that's what I suspected... :-(

> Neither should the sense pin be grounded. The poster who mentioned a
> bios setting to disable the fan error-stop was correct.

Good idea, but the power to the machine cuts out after a fraction of a
second, so it's not an option.

Given that (supposedly) an Athlon without the heatsink can fry in
under a second(!!), this is not surprising, but it does mean I can't
do anything with the BIOS.

- Michael S

On 6 Oct 2003 03:41:52 -0700, (Michael Strorm)
wrote:

<snip>

>> Neither should the sense pin be grounded. The poster who mentioned a
>> bios setting to disable the fan error-stop was correct.
>
>Good idea, but the power to the machine cuts out after a fraction of a
>second, so it's not an option.

I'm surprised the bios doesn't display a warning for a bit before that
happens. You don't have ANY fans with RPM you could attach to the
header just long enough to enter BIOS setup and change that setting?
Doesn't necessarily need to be sitting on the heatsink, just plugged
into the appropriate fan header. Perhaps another chassis or PSU fan
has the tach-output (RPM signal) feature, so you could temporarily
sway these fan plugs from their respective headers?

>Given that (supposedly) an Athlon without the heatsink can fry in
>under a second(!!), this is not surprising, but it does mean I can't
>do anything with the BIOS.

True, but that's only without the heatsink itself... with the heatsink
on but no fan it'd run for at least dozens of seconds, maybe several
minutes before locking up (depending on other factors), and the temp
increase rate would be slow enough that the motherboard temp shutdown
feature could react and shut down the system.


Dave

Michael Strorm wrote:

> Hi,
> Is it possible to fool a motherboard into booting even without the
> fan attached (assuming it checks the rotational speed before
> proceeding)?
> I thought shorting the 'SENSOR' and 'GROUND' pins would work at
> first, but if it's being used to detect the fan speed, then maybe not?
> The CPU_FAN connector on the Gigabyte motherboard has 3 pins
> (SENSOR, 12V and GROUND), if that's relevant(?).
> Any help would be appreciated, thanks!
>
> - Michael Strorm
You can turn the protection off in the BIOS, where it's labelled
Guardian Function. You'll just need something connected enough to get it
to the BIOS.

Barry Walsh wrote:

> Michael Strorm wrote:
>
>> Hi,
>> Is it possible to fool a motherboard into booting even without the
>> fan attached (assuming it checks the rotational speed before
>> proceeding)?
>> I thought shorting the 'SENSOR' and 'GROUND' pins would work at
>> first, but if it's being used to detect the fan speed, then maybe not?
>> The CPU_FAN connector on the Gigabyte motherboard has 3 pins
>> (SENSOR, 12V and GROUND), if that's relevant(?).
>> Any help would be appreciated, thanks!
>>
>> - Michael Strorm
>
> You can turn the protection off in the BIOS, where it's labelled
> Guardian Function. You'll just need something connected enough to get it
> to the BIOS.
>
It just occured to me that this may also exist as a jumper rather than a
BIOS option.

>> - Michael Strorm
>You can turn the protection off in the BIOS, where it's labelled
>Guardian Function. You'll just need something connected enough to get it
>to the BIOS.

Some motherboards default to this protection being OFF. Mine does, and
I know this works because it is a watercooled system with no fans
connected to the motherboard headers, and I have discharged the cmos
afted updating the bios, and never had to use a fan or anything to get
into the bios. I'd try discharging the cmos, or boot with default
settings and see if it works.