I just relaced the fan on a Zalman 7700 CPU cooler that is on a LGA775 CPU. The mobo is an Asus P5B-E.

The new fan that I used was a Arctic 12 PWM with a four pin connector and it had a second single wire that attaches somewhere. The original Zalman fan only had a 3 pin connector. I could not connect the new fan to my fanmate controller as it would only accept three pin connectors.

Upon rebooting I got a BIOS error - CPU fan failed. But I could see that the fan was working and upon booting up it was fine. Temps looked fine as well. But Speedfan also didn't see the fan as it wasn't reporting a speed. Therefore I couldn't really control the fan speed.

I found another Fanmate controller that I had around that had an open type of connector so it could accept the four pin connector. I added that and rebooted again. I still get the CPU fan error but at least I could control the fan speed and noise, albeit mechanically. I have shut off the CPU error notification. The system seems fan - idle core temps are 30C or so and after running Prime95 for 30 mins I get up to 60C (according to SpeedFan) and 64C acording to CoreTemp. Those are a bit high but I am not too worried since I don't really do hardcore stuff on this computer.

A few questions:
Why does my mobo not see the fan? Is it a bad idea to use this fan as a CPU fan? What is the other lead for on the CPU fan? Should I connect this somewhere? Is this supposed to be connected to the CPU fan connector on the mobo?

This photo below isn't exactly what I have on my new CPU fan, but it does show the connector with the single wire. What do I do with the single yellow wire connector on the left in this photo - where does it go?

It looks like your motherboard is unable to read the RPM signal from this 4-pin fan, that's all. This is unusual, it tends to be the other way round with 4-pin headers not working properly with 3 pin fans.

As 4 pin fans tend to be more expensive and have a more limited choice than 3-pin I would suggest you get a replacement 3-pin on there to get your RPM readings back if it's really that much of an issue.

I am wondering if that 3 pin single wire connector give the RPM reading to the mobo? But if so I wonder where I would connect the main 4 pin connector? To another fan header or maybe (via an adapter) to a molex connector.

Replacing the fan is a bit of a PITA so I don't know that I want to do that again if I can avoid it. Maybe I will try plugging that other connector into the CPU fan header and see what I get.

Ah, maybe I misunderstood you. I thought you'd already tried that! Connect the yellow wire to the header that you want to sense the RPM on. Yellow tends to be for RPM. Then you need to power the fan from another header or use a fan splitter cable. Alternatively you could rewire the connector. Disconnect the + and - wires from the 4 pin header and connect them to the corresponding positions on the 3-pin connector. You would need a fine screw driver to release the crimp connections from each hole in the 4-pin connector.

No just somewhere, the single yellow (RPM detecting) wire needs to be plugged into the extension socket on the F12 motherboard connector. In your graphic that is the connector on the right. Not doing this will generate a BIOS error because the motherboard will detect that a PWM fan is present but a fan rpm signal will be absent.

The reason for the separate yellow wire is that Arctic use a system called PST (PWM Sharing Technology). This allows Arctic PMW fans to be chained together without needing a separate cable. But as PWM sharing of any form needs the RPM signal carried on the yellow wire from only one of the fans on the chain Arctic opted to give each fan a separate RPM sensing wire and connector. So if you were chaining another fan or fans to the CPU fan you would plug all the connectors into the extension sockets. Then on the last fan in the chain the yellow sensing wire would be connected to give a PWM fan chain with only one RPM monitoring source. But for a single CPU fan setup the yellow wire connector is plugged into the PWM extension socket on the same fan. From what I remember the instructions provided by Arctic did not really explain this particularly clearly.

Thanks that explains a lot. However my fan did not have the extension connector on the right to facilitate daisy chaining, it just had a basic four pin connector and the separate yellow lead. Should I just cut the yellow wire off the 3 pin connector and try to attach it to the existing four pin connector in the right spot, which would be the leftmost position on the 4 pin connector when looked at from the front as in the above photo? Or try to find another extender?

I guess I could just attach the 4 pin to a molex connector or to the unused Chasis 2 header and the 3 pin to the CPU header but then you get a screwy situation since I would have to adjust Chasis 2 in speedfan to control the speed which would then show up as the speed of CPU fan.

You might get "a screwy situation" in the BIOS Hardware Monitor, but in Speedfan you can rename the labels to whatever you like.

Yes, that's possible. It's been a while since I setup Arctic F12 PWM fans and at that time they had the extension socket but I note that Arctic now sell a separate PST cable. So it seems to me that this is probably more of a BIOS configuration issue that anything else. With the F12 plugged into the CPU fan header I would suggest that you enable CPU Q-Fan Control in the BIOS and set the CPU Q-Fan Profile to Silent. You also need to set the CPU Fan Speed to Ignored. That might seem a bit curious but it is the correct setting for a fan like the F12 which runs under around 600 rpm. You may already have done this, not doing it generates the BIOS CPU Fan Failed error that has already been seen. (In later BIOS releases for other motherboards Asus provided a separate Minimum CPU Fan Speed setting, set by default to around 600 rpm and including an Ignore option).

Next uninstall SpeedFan and download from the Utilities section on the Asus website the Ai Suite V1.02.05 utility. The Ai Suite includes the Fan Xpert software which will show the current CPU fan profile graphically and report the current CPU fan speed. There is also a Calibrate option which will show the CPU fan speeds for the 20% to 100% duty cycle range. Fan Xpert works even if the BIOS CPU Fan Speed is set to Ignore.

Thanks Lodestar. The OS on this PC is Win7 Home Premium 64 bit. The download page doesn't have Win7 as an option, I am assuming that the Vista 64 bit would be the way to go? I think I tried this in the past but got something like unsupported OS when running the install, but I will try it again.

I think may even have the original CD for the system.

Do I really have to uninstall Speedfan? If I just use it for reporting purposes, and not to adjust fan speeds is that an issue? I use Speedfan to feed temperature status to Rainmeter so that I can monitor CPU temp.

Yes, it seems that Asus do not support Windows 7 on motherboards like yours which use the Intel P965 775 chipset. There is support for Win 7 on the slightly later boards which used the next generation of Intel 775 chipsets such as the P45 based P5Q. It might be worth downloading the P5Q version of Asus Ai Suite for Win7 64 and seeing if that works. If not the only alternative is SpeedFan. The reason for the comment about uninstalling SpeedFan if using Fan Xpert was only to avoid any chance of a conflict from the two being present at the same time. Also Fan Xpert needs Q-Fan Control to be enabled, with SpeedFan it needs to be disabled.

I didn't have a chance to open my case last night and check out the connectors again.

Would it be a bad idea to pull the yellow wire off of the 3 pin connector and attach it to the correct spot of the 4 pin connector? That way I would just attach the F12 to the CPU Fan header and it should be able to read the speed as well.

That's what I'd already suggested but the other way around by moving the + and - pins over to the 3 pin. That way you don't have a non-PWM 4-pin header which would be very confusing.

Yes, that has been carried out where the PST connection socket and separate yellow RPM wire were not required. This is an example of how it was done.

Thanks Lodestar, that is what I will do. In the photos it looks like he is doing the crimping with an exacto knife. Is that how he is doing it?

@edh - Maybe I am misinterpreting what you are saying but it is a PWM fan, is it not? It is just that the Yellow RPM wire is made to connect to a different header and/or to facilitate the daisy chaining of fans.

Doing the mod that Lodestar linked to then don't you end up with standard wiring for PWM fans?

Yes, hence why it is better you have a +, - and RPM channels on a 3-pin header, not a 4-pin header. On the 4-pin header would be confusing as that is generally for PWM connections and by doing this you won't have a PWM connection. Oh nevermind, just so long as you find a way that works.

My bad!

I finally got around to opening up my case again and the fan did have the piggyback connector so I plugged the 1-wire yellow 3 pin connector into this and the CPU fan is no reported. I don't seem to be able to control the speed with Speedfan and I am not sure about the Asus Q-fan so I am using a fanmate controller. Cranking this all the way done give me about 650 RPM and it still manages to cool the CPU well, even after running Prime95 for over an hour. And at this setting the system is almost silent as I have the case fan also below 1000 RPM.

Before replacing the fan, did you try lowering the minimum CPU fan speed in the BIOS? Or disabling CPU fan control in the BIOS?

I had the same error last week when I installed my NH-L12 and learned that the minimum rotating speed caused the error. The fan was getting down to 200rpm on boot and my motherboard (Asus P8Z77-M Pro) didn't like it. I went into the BIOS and noticed the CPU fan was set at a 600 rpm minimum. I changed the minimum to 200rpm and everything worked fine. I haven't had any issues since.