Z400 rear chassis fan always running at high RPM

[VinceO]

I have several Z400 workstations. One of them is significantly noisier than the rest: the rear system fan (chassis fan) is almost always running at high RPM. On the normal Z400s, the BIOS Setup | File | System Temperatures reports chassis fan speed of about 1600 RPM. On the noisy Z400, the chassis fan speed is reported as 3752 RPM. Both Z400s are running the latest public BIOS, 3.57. Both have BIOS Setup | Power| Thermal | Fan Idle Mode set to 1. Cycling Fan Idle Mode from 1 to 5 on the normal Z400 makes a huge difference in fan RPM. Cycling from 1-5 on the noisy system barely makes any difference.

How can I quiet the chassis fan in the noisy Z400? I’ve carefully vacuumed the inside of the Z400, including removing the air cover that shields the DIMMs. If it matters, the Z400s are running Windows 7 Pro with all the latest patches.

I notice that BIOS Setup | File | System Temperatures reports an Ambient temperature of 23C on the normal Z400 and 0C on the noisy Z400. Is there any chance that “Ambient temperature 0C” means the ambient temperature sensor is broken, and without knowing what the temperature is, the BIOS runs the fan at full speed no matter what? If so, how would I debug/fix this?

Thank you.

[SDH]

I had a similar issue with a xw6600 that was solved by replacing the cable unit that carries the ambient air temperature thermisitor, which was reading way too high.  It may be that reading way too high or too low is set as an indicator to the motherboard that something is amiss with the thermisitor (creative HP engineering, if so), and the motherboard's fan contoller may be programmed to ramp up the fan speeds in both cases.  Here is the link:

/t5/Workstations-z-series-xw-series/xw6600-xw8600-fans-way-too-fast-and-loud-solved/m-p/5426247#M128...

I do like HWMonitor, from CPUID.com, as a free program for probing fan speeds and temperatures of different parts of the HP workstations.  The success of these types of programs varies depending on the sensors involved, but it is worth a try.  The purchase version adds some bells and whistles, but does not seem to detect more sensors, in my experience.

Keep us posted on this project, please.

[SDH]

Here you go with some parts numbers.... there can be an assembly part number and a spares part number for the same part.  Search under both on eBay and Google if you have access them.  Good luck.  This is a rare event and thus of significant value if you get to the solution, so let us know what you find.  That top pic with reference to the thermisitor is from HP.

I was very relieved to get rid of the SuperFan noise in that xw6600.....

HP how-to-do-it:

http://h20566.www2.hp.com/portal/site/hpsc/template.PAGE/public/kb/docDisplay?javax.portlet.begCache...

[VinceO · Accepted solution]

Scott, you are exactly right.

I replaced the power on/off switch and LED cable assembly, which includes the thermal heat sensor, on the noisy Z400 with one taken from a normal Z400. The noisy Z400 is now normal, with a rear chassis fan running at about 1700 RPM. The BIOS reports the Ambient air temperature correctly at 23C.  HP's “how to do it” instructions for the cable replacement were quite good. Now all I need to do is order another good cable assembly.

Scott, thank you very much, for the prompt diagnosis and helpful links. This issue is SOLVED. Thanks again.

[DANNY_BEKEREJIA]

I HAVE THE SAME PROBLEM AND I ONLY REPLACED THE TRANSISTOR IN ANOTHER PLACE BECOUSE ONE OF ITS TWO CABELS WAS HITING THE METAL

THANKS IN ADVANCE HP