p2b-d and antec sl400

[William Katz]

About three weeks ago I upgraded the power supply in my computer to an
Antec SL400 (400 Watt). Everything is fine, except one minor quirk I
noticed. The power fan RPM is not detected in the BIOS (or ASUS Probe
v2.22.03).

Here are my specs:

ASUS P2B-D Rev. 1.06 (D01)
ACPI BIOS Revision 1014 Beta 003
512MB RAM (2x256MB SDRAM PC-100)
DUAL Pentium III 850Mhz Slot 1 CPU's (100Mhz FSB)


I have cpu #1 3-pin fan cable connected to the cpu fan connector on the
motherboard, cpu #2 3-pin fan cable connected to the chassis fan
connector, and the power fan cable from the SL400 connected to the power
fan connector.
The power fan cable on the SL400 has 2 wires on it (black and blue). Maybe
the power fan connector on the P2B-D must have 3 wires connected to it?

By the way, if I switch the power fan cable to the chassis fan connector,
that gives a proper RPM readout in the BIOS.

Does anyone have a solution to this minor problem?
TIA

 

[P2B]

About three weeks ago I upgraded the power supply in my computer to an
Antec SL400 (400 Watt). Everything is fine, except one minor quirk I
noticed. The power fan RPM is not detected in the BIOS (or ASUS Probe
v2.22.03).

Here are my specs:

ASUS P2B-D Rev. 1.06 (D01)
ACPI BIOS Revision 1014 Beta 003
512MB RAM (2x256MB SDRAM PC-100)
DUAL Pentium III 850Mhz Slot 1 CPU's (100Mhz FSB)


I have cpu #1 3-pin fan cable connected to the cpu fan connector on the
motherboard, cpu #2 3-pin fan cable connected to the chassis fan
connector, and the power fan cable from the SL400 connected to the power
fan connector.

Maybe your board is labelled differently to mine, but I would expect cpu
#2's fan to be connected to the power fan connector because it is much
closer to the CPU.

The power fan cable on the SL400 has 2 wires on it (black and blue). Maybe
the power fan connector on the P2B-D must have 3 wires connected to it?

Normally a monitored fan will have 3 wires: +12v input (red or yellow),
ground (black), and RPM sense output (blue or green). It sounds like the
power fan is supplied with +12v inside the power supply, and only has
ground and RPM sense externally. It's probably designed that way so the
fan runs without requiring a connection to the motherboard.

By the way, if I switch the power fan cable to the chassis fan connector,
that gives a proper RPM readout in the BIOS.

In that case either the RPM sense input for the power fan connector is
dead, or the connector orientation is backwards. Does the cpu #2 fan
give an RPM readout when connected to the power fan connector?

When looking at the board from the front (where drives connect), the
plastic locator tab on the power fan connector should be to the right of
the pins. First pin from the front is ground, middle pin is +12v, and
RPM sense is the rearmost pin.

HTH

P2B

 

[DaveW]

Correct; it must have 3 wires.

 

[P2B]

Maybe your board is labelled differently to mine, but I would expect cpu
#2's fan to be connected to the power fan connector because it is much
closer to the CPU.



Normally a monitored fan will have 3 wires: +12v input (red or yellow),
ground (black), and RPM sense output (blue or green). It sounds like the
power fan is supplied with +12v inside the power supply, and only has
ground and RPM sense externally. It's probably designed that way so the
fan runs without requiring a connection to the motherboard.



In that case either the RPM sense input for the power fan connector is
dead, or the connector orientation is backwards. Does the cpu #2 fan
give an RPM readout when connected to the power fan connector?

I was messing around today and learned of a more probable cause of your
problem - the BIOS will not display fan speeds below a certain RPM,
instead it displays xxxxRPM [ERR] regardless of whether the fan is
spinning slowly or not at all. I suspect the BIOS 'tolerates' a slow
chassis fan but not a slow CPU or power fan, which would explain why
your power fan only registers when connected to the chassis fan
connector. I suggest ignoring the BIOS readings for now and checking
your fans with Motherboard Monitor, which will display the actual RPM at
all speeds and let you decide when the fans are too slow.

I had planned to determine what the BIOS speed thresholds are, but
unfortunately I was testing with a 2-wire fan I had just added an RPM
sensor to - and wired it wrong :-( Now my chassis fan sensor is dead and
I'll have to replace the sensor chip before I can proceed.

 

[William Katz]

Maybe your board is labelled differently to mine, but I would expect cpu
#2's fan to be connected to the power fan connector because it is much
closer to the CPU.

Yeah, I had that originally before replacing the power supply. When I put
in the SL400, I attached the fan wire to the chassis fan connector on the
motherboard, and it reads the rpm speed, but gives that 'error in bios,
press f1 to bypass....' on system start, since like you said maybe it is
below the threshold for chassis speed. So, I switched it with cpu #2 fan.

Normally a monitored fan will have 3 wires: +12v input (red or yellow),
ground (black), and RPM sense output (blue or green). It sounds like the
power fan is supplied with +12v inside the power supply, and only has
ground and RPM sense externally. It's probably designed that way so the
fan runs without requiring a connection to the motherboard.


In that case either the RPM sense input for the power fan connector is
dead, or the connector orientation is backwards. Does the cpu #2 fan
give an RPM readout when connected to the power fan connector?

Yes, all fan connectors (cpu#1, cpu#2, and antec sl400 power supply) give
rpm readouts, with the only exception that if the power fan is connected
to the power fan connector, there is no rpm readout "xxxxRPM [ERR]" in
bios. The fan works though, it is spinning. It shows around 1600 rpm
when connected to the chassis fan connector on the motherboard.
I guess i'll just install motherboard monitor and see if it shows up in
there. Thanks.

 

[P2B]

William Katz wrote:
[snip]

Yes, all fan connectors (cpu#1, cpu#2, and antec sl400 power supply) give
rpm readouts, with the only exception that if the power fan is connected
to the power fan connector, there is no rpm readout "xxxxRPM [ERR]" in
bios. The fan works though, it is spinning. It shows around 1600 rpm
when connected to the chassis fan connector on the motherboard.
I guess i'll just install motherboard monitor and see if it shows up in
there. Thanks.

It will. I determined the BIOS thresholds for the chassis fan connector
are 1800 rpm (shows rpm [ERR] below 1800) and 1400 rpm (shows xxxx [ERR]
below 1400). I haven't determined the exact thresholds for the other
connectors yet, but they are definitely higher. Motherboard monitor
shows actual rpm no matter how slow it is

 

[William Katz]

It will. I determined the BIOS thresholds for the chassis fan connector
are 1800 rpm (shows rpm [ERR] below 1800) and 1400 rpm (shows xxxx [ERR]
below 1400). I haven't determined the exact thresholds for the other
connectors yet, but they are definitely higher. Motherboard monitor
shows actual rpm no matter how slow it is

I'm guessing the threshold for the power fan connector is somewhere above
1600 rpm?

By the way, do you know where I can get a P2T thermal cable? I found one
for $9.50. If you think that's a fair price, I'll get that.

 

[P2B]

It will. I determined the BIOS thresholds for the chassis fan connector
are 1800 rpm (shows rpm [ERR] below 1800) and 1400 rpm (shows xxxx [ERR]
below 1400). I haven't determined the exact thresholds for the other
connectors yet, but they are definitely higher. Motherboard monitor
shows actual rpm no matter how slow it is

I'm guessing the threshold for the power fan connector is somewhere above
1600 rpm?

From vague memory it's 1800rpm, but I haven't gotten around to
verifying the exact thresholds yet.

By the way, do you know where I can get a P2T thermal cable? I found one
for $9.50. If you think that's a fair price, I'll get that.

You can make one using a 10K ohm thermistor and the 2-pin header from an
ATX reset or power switch for a dollar or two - just cut the leads from
the header to the required length, solder on the thermistor (doesn't
matter which way around) and insulate the connections with plastic
tubing (the heatshrink variety is preferred).

Alternatively, I have several homemade ones on the shelf because I had
to replace them with tiny axial-lead thermistors when I switched to S370
processors. Yours for $US4.00 each including postage, email me if you
want one.

P2B