HPZ840 Fan noise

[mhx4]

My (refurbished) HPZ840 with Windows 10 Pro works flawlessly, but the noise level is horrible (like a vacuum cleaner). I sounds like the fans are running at full speed, even if no significant work is done.

A post by Miloman a few years back described this same problem, and he 'fixed' it by removing the CMOS battery and resetting. I will of course try that solution, but why does it help at all? Or is there a fan-profile set in the BIOS that can wander away?

-marcel

[SDH]

BIOS corruption is a real thing. You may not know that there is a BIOS setting for baseline fan speeds. It is set to the lowest value at the factory but can be shifted upwards IIRC 5 more steps. If you bought that used then a prior owner may have shifted it up in speed and perhaps you've had that set too high the whole time? Some people do that for times of very high processor work such as during video rendering.

There is a way to capture your current settings as a .txt file via BIOS/ Replicated Setup/ save to thumb drive. You can archive that and even review the different settings from that file. My instinct is that if BIOS is corrupted the corruption may not show up in the .txt file, however. I keep an archive of my complicated changes to BIOS for certain of our workstations so I can easily get back to what I did months ago if something got changed.

Yes, BIOS can get corrupted rarely to the degree that a "deep" level of CMOS clearing is needed to clean up the mess, rather than a simple push of the yellow motherboard button. DGroves has posted here on how to do that, how to confirm that it really happened, and when a workstation starts acting wacky enough that is one of the things may end up having to do.  It gets your BIOS back to "factory defaults".

[DGroves · Accepted solution]

the z800 through 840 systems have what's called a ambient air temp sensor that is embedded in the power switch/speaker cable

this sensor when failed will cause the case fans (usually not the cpu fans) to ramp up to full speed and stay there

to test for this, enter the bios and check the "system Ambient Temp" value if it's very high the sensor has failed

you can replace just the sensor or the entire cable to resolve the problem

https://www.amazon.com/HP-Power-Button-Speaker-644320-006/dp/B015YQK1GC

i've previously posted details on this several times on this use the forums search feature to locate them

here's part of a previous reply i posted

=================================================================================

if  replacing the sensor in the cable, it's near the power button board end close to where the speaker wires exit the black heat shrink that covers the cable wires , and it's a common npn transistor you can use a 2n3904 or a 2n222a plastic body transistor as a replacement

note that the existing transistor will have two leads connected together and a single lead connected to colored wires,  match the existing leads  to the replacement and also note which lead connects to which color wire

https://components101.com/transistors/2n2222a-pinout-equivalent-datasheet

[mhx4]

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[mhx4]

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[mhx4]

> enter the bios and check the "system Ambient Temp" value

> if it's very high the sensor has failed

I can't find this setting in the HPZ840 bios :--(  However, the fact that the fans are quiet when playing with the BIOS, and start howling a minute after booting Windows 10, perfectly matches your diagnosis.

Unfortunately, replacing the speaker/power switch cable means that the right side panel of the housing must come off. From the online manual video it seems a lot of work. Replacing the 2n2222 might be simpler indeed.

[mhx4]

Thank you! However, the BIOS fan setting is at its lowest and still the fans go to maximum about one minute after booting in Windows 10. For now, the diagnosis by Dgroves looks more promising.

I found the option to save settings to USB stick, that might be useful sometime.

[mhx4]

For my Z840, the cable that connects the speaker to the motherboard is not combined with the cable from the power switch. ( I can't get to this power switch yet, but it seems to be directly soldered on a rectangular pcb together with the USB ports. The Amazon link shows a very small pcb with only the switch. )

However, there is indeed a transistor right at the entrance of the shrinktube that takes the speaker cable to the motherboard.

[SDH]

My recall is that DGroves (who knows these things) once posted that the Z820 speaker and power on/off switch cable also works in a Z840. Use google to search for 

HP Z820 Power Button with Speaker New 644320-005

That is from the Alan guys, who have treated us well. You might also want to call them.

You may be across the pond but at least in the US eBay listings you can find that part number too. I've posted in our forum on how to get the right-hand side panel off but I think you don't need to do that for this repair. I've replaced these in the Z420 and Z620 workstations but if IIRC the Z820 one is a bit longer. I've done that in the past using both a new replacement and used ones (a bit higher risk). It is pretty rare for these to go bad, and kudos to DGroves for remembering the issue. The motherboard gets bad info from that embedded transistor, out of specs either high or low, and responds with high fan speed to protect the motherboard. Sometimes you can see the detected ambient temp way off using HWMonitor (good free utility from CPUID.com. You don't need the Pro version). The transistor for some workstations is embedded in the cable under heatshrink, and in others it is on a little side pigtail that you zip tie to the case metal. Mark on the metal grill where that was if you do this so you can get the new one back in the right position.

[mhx4]

>> I've posted in our forum on how to get the right-hand side panel

>> off but I think you don't need to do that for this repair.

I certainly had to! The speaker is in a tiny cabinet and my hand is way too big to fit in there. Once the connector is severed, the cable can be pulled out and very easily inspected for the 2N2222.

Alan Computech's offering is quite probably the right cable, indeed. I could not remove the front panel yet (no proper Torx screwdriver). With what I disassembled sofar, the power switch is in front of a rectangular pcb that mounts all the USB ports and audio.

>> Sometimes you can see the detected ambient temp way off using HWMonitor (good free utility from CPUID.com.

Thanks, I was afraid that the temperature sensor contraption was an HP special... I'll need HWMonitor to peek at the 44 cores data in this beast for sure.