Z840 CPU1 fan too high speed

[Foby71]

Hallo,

Got a Z840 workstation a week ago. It worked fine till yesterday. Very quiet. Fans set at minimum by bios (I mean  lower speed setting)

Then I made a big bul**bleep** to turn on the unit without the cpu/memory fans plastic chassis. It went in error cause it felt that no fans was connected. I suddenly switched off the unit and then I put back the fans chassis. 

Now, it works but the CPU1 fan always run at more than 3000 rpm while the other runs at 1000 more or less.

No way to modyfy.

Only if I take out and put back again the fans chassis while the unit is ON, the fans start to work normally (also CPU1 goes arount 1000).

Bios 2.50

I read some discussions about similar problem, but no one was explaining what happen clearly.  Could it be a fan problem?

Could I try to invert CPU1 fan and CPU0 fan to se if the problem is inverted?
How is exaclty the control on those 4 wire fans?

[DGroves · Accepted solution]

do a full cmos reset, (backup existing custom settings)

remove power cord, press power button for 15sec

open side cover, remove cmos battery, (optional, then press cmos reset button) wait 10min

replace battery power on, enter bios set date/time and any custom settings

if still having a problem, re-apply cpu paste on cpu 

if still a issue, replace the cpu-1 cooling fan in the shroud

the 5 pin cpu fan header follows the normal pc pwm fan pinout (pins 1-4) with pin 5 used to detect if a high performance heatsink/fan is installed (wire going from pin 5 to pin 1)

all of the above can be found in the HP z840 "Service Manual" located on the hp site (google for it)

[Foby71]

h! Thanks!!

I did it the cmos reset just before to read your reply and it worked fine.

I remembered it as most famous computer bios recovery solution and I tried myself.

Switched all off, removed everything excluded CPU/RAM and video card, then removed the battery.

Left without battery half an our (dinner), then I reinstalled all and it work fine now. no anymore too speed CP1 fan.

Probably it was set previously some strange flag into bios which couldn't be deleted by norma factory deafult selection.

Many thanks

For me it is finally solved.