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HP Recommended
Microsoft Windows 7 (64-bit)

Hello, i whant to know are there any problem with my PC, or z420 motherboard just don't have any fan rpm sensor.

I tried Aida64 and speedfan programs and don't find any mention of fan rpm((

May be i need some extra drivers?

I have 3 and 4pins fans, i tried conect both to motherboard fan connector. Both of them spinning at full speed, this is quite noisy((.

So, for decreasing the noise i connect 12v fan pin throw resistor to 12v molex hdd power pin, and have good rpm and low noise. To bypass f1 fan not detected, i use wire from fan rpm pin to motherboard fan rpm pin.


But i whant have auto adjust speed of fan depending of cpu load.

I'd be grateful for any help.

HP Recommended

the HP z series workstations do have a motherboard fan sensor circuit for the case fans, but the ambient tempture sensor part is embedded in the HP power cable, this sensor is a common npn 2n222a T0-5 plastic part


you can buy a pwr button assembly off ebay and carefully remove the black heatshrink wrapping to expose the sensor, and follow the 2 wires down to the header on the motherboard. make sure to not swap the wires!! if you do the sensor will not work and may need replacement

HP Recommended

Thank you!)

May be i can use simple resistor to replace ambient sensor?

I don't need to know real case temperature, because my case always open)

So i want just cpu fan speed adjustment is working

i found this thread https://www.eevblog.com/forum/beginners/removal-of-npn-transistor-being-used-for-temp-monitoring-(si...

and there is post:

"Here is an article that explains what Hess is describing: http://www.analog.com/media/en/analog-dialogue/volume-33/number-1/articles/measuring-computer-chip-t...

If you want to replace the 3904 with a resistor, look to see what chip is processing the deltaVBE and see what currents are being applied.  Then calculate the resistor value. The ADM1021A uses 205uA and 12uA thus 0.026*ln(205/12)=74mV ->> 74mV/(205u-12u) = 382 ohms"


so i whant to try 382ohms resistor, is it safe for motherboard?

HP Recommended

You have a rats nest of wires in there.  Don't expect things to work normally when you are:


1.  Using a non-HP power supply

2.  Have two single wires running to at least two of your motherboard's fan headers.

3.  Using a non-HP CPU heatsink with a non-HP 3-wire lead to its 3-wire fan.  That heatsink fan is supposed to be properly wired to the motherboard's 5-pin header.  I'd start by getting a HP CPU heatsink fan with 5-pin plug for that.  That probably takes a 92x25mm fan, and HP has both those and 92x15 with the 5-pin plug.

4.  Components in a HP case are designed to run cooler with the case sides on.  That is not a HP case.


The HP motherboard is programmed to protect itself when it sees chaos in the cooling ecosystem, which you surely have, and responds by trying to save you by running the fans at full speed.


You're the guy who wants to overclock........ try starting by buying some proper HP fans, new or used, with their correct plugs connected to the correct motherboard headers.  The free HWMonitor program from CPUID.com is worth getting but I don't think it will be able to make sense of what it will see.  HP Performance Advisor is free too, but will be confused also..

HP Recommended

SDH thank you for reply, hp 5 pin fan as i know is just usual 4pin fan with wire from 1 pin to 5pin. I tried to connect all 5 pins in motherboard this is not helped(

DGroves posted i think good reason why fan is in full speed "ambient tempture sensor" if this will not help i will try your suggestions.

Are you have z420 motherboard and HWMonitor show fan RPM??

HP Recommended

Regarding the ambient air sensor DGroves is an expert on that.  If you have all the proper fans properly wired and the set of fans all start going too fast then that sensor is what almost always is the cause.  You must, however, not have a mishmash of non-hp fans and strange fan wiring.  Once the motherboard sees that it has to assume something is wrong and defaults to ramping up all the fans.


I have seen the ambient air sensor read falsely too high and falsely too low, and saw that using HWMonitor.  In both situations the fans speed up.  The default in all cases of mishmash is to speed up so don't start by assuming the sensor is bad in your situation.  I'd bet it is fine and that it is your other creative wiring that is at fault.


Yes, I do have a few Z420s I'm working on a project with.... the free version of HWMonitor works fine on those.  Just download it and take a look.  If I have time I'll grab a screenshot of it in action in a Z420.  Don't get me wrong.... I have respect for Ghetto Mods, and do some myself.  But I do believe you are over the top here.

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I tried HWMonitor earlier and it can't see fan rpm(( But because your suggestion i go to their official site again and download trial pro version - it is not helped((Screen Shot 10-22-18 at 11.49 AM.PNG

But HP Performance Advisor do the job!) It can see fan rpm) Thankyou!) Also i can see system ambient sensor is at 128 degrees!)

Screen Shot 10-22-18 at 11.39 AM.PNG

  HP Performance Advisor

HP Recommended

No, you can not use a resistor in place of the transistor, and said transistor is wired to make the transistor  junction behave as a diode it's wired as follows:



Collector and Base leads connected together (pin 11 on z800)  Emitter (pin 12 on z800)
for your z420 consult the service manual for proper temp sensor pins as they may not be the same as the z800



I second "SDH's" recommendations what you now have might be ok for a proof of concept but is not something to leave as is for long term


i had one z800 where the motherboard temp circuit failed and replacing the sensor would not work for that system, i used a 10 watt rheostat on the fan pwr line till i found the value that gave a slightly higher speed than HP's default fan speed (52 ohm) i then bought two ready made 4 pin one watt 52 ohm PWM fan speed reducers off ebay for the front two fans, and seperate 5 watt resistors for the memory and rear case fans which are each dual fan setups using a common pwr line


last, leaving a case open usually decreases the cooling effect of any fans mounted in said case, however many cheap and not so cheap cases don't cool well anyway


HP spends a lot of time designing a case/fan setup for a workstations  proper cooling under the systems rated temp range. and case replacements using 3rd party cases will almost always not be as good overall as the HP solution

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Thank you, i will try it)

My PC most of time is iddle, and i whant from it real noiseless work.

A lot of fans - is quite noisy((

But i think to get some small fan over VRM part of motherboard to cool it down when computer is in hard work. Maybe i will make some extra circuit for this fan, to get it work only when cpu is working(hot)

Also i wonder why  HWMonitor can't see any fan?? What driver can be respond for this?

HP Recommended

i beleive HWMonitor will read the fan rpm, but you need to setup a custom profile telling it the correct settings.


read the programs documentation

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