Fan assembly fans running at full speed

[SailorJeffrey]

Good Day,

The fan assembly fans (from part 642166-001) of my Z820 are constantly running at full speed.

I have confirmed this is indeed the case against another Z820 running correctly.

Idle fan speed set at minimum in BIOS.

BIOS updated to v3.94

Ambient temperature reading 20 C, therefore error not caused by faulty power switch harness.

Fan assembly has been switched out with another Z820 which has rectified the fault.

What could be within the fan assembly that is causing the fans to run at full speed?

[DGroves]

the most common cause of fans ramping up to full speed during the bootup is a bad temp sensor reading which is usually the ambient sensor in the power cable

however try these things first

what cpu's are installed? 130 watt ones require the high performance 3 heatpipe coolers 150 watt cpu's require the water cooling option   95 watt cpu's or lower  can use the stock low performance 2 heatpipe coolers

try resetting the bios to factory defaults (not the user saved defaults but the factory defaults)

then try reseating the cpu coolers and checking the coolers for correct thermal past xfer between cooler/cpu

still fan issues? , boot the system and then remove the power switch cable from the motherboard connector do the fans still run as  fast? now reconnect connector do the fans slow down  if not either the sensor or the motherboard circuit may be bad

[SailorJeffrey]

Thanks for getting back to me.

I have dismissed a bad ambient temperature sensor as I have checked ambient temperature and is is reading correct.

Further fault finding... I removed the fan assembly from a machine that is running correctly and swapped them out. It runs correctly. I replaced the original fan assembly and the fan is running at full speed which tells me the fault lies with the fan assembly. Furthermore I have identified that it is only one single blower that is running at full speed. It is the blower (not fan) for the memory at CPU 0.

What within the fan assembly could be causing this blower to run at full speed?

[SDH]

DGroves has a Z820 and more knowledge on the internals of the thermisitor/ambient air temp issue than I do.... but here is an idea:

HP, for their 4-wire PWM fans, has traditionally chosen quite fast fans and then applies strong PWM control from the motherboard back to the rotor.  I've thought they did that to allow a strong ramp up in speed if needed, and to get the best bearings.  The speed control is not by varying the voltage.... it is by applying more or less PWM braking.

I'm assuming the blower type fans also are chosen this way, assuming they also are PWM controlled fans.  If the PWM circuitry in the rotor of your blower died then your fan will act like a 3-wire non-PWM fan receiving full 12VDC, and run at full speed, at all times.  I have done this experiment by temporarily removing the PWM control wire from a number of good HP PWM controlled 4-wire fans from HP workstations.  The fans run quite fast and loud that way, and the reason I did it is below.

I think that your blower type fan has lost its PWM circuit functionality, and that you need to find a replacement.  It is better to lose that at the fan than on the motherboard.  Often a HP part number is on the label on the fan face that is in the direction of air flow.  You often need to remove the fan from its holder to see that face.

I have been able to find non-HP equivalent fans for specific HP fans from the same OEM HP supplier by using the supplier's codes present on the HP fan labels... on searching with Google some of those have had PDFs showing the whole family in that group with their 12V RPMs listed by the codes.... for example, LL, ML,  L,  M,  MH,  H,  HH.  Then I could match the 12VDC RPMs to see what HP had selected as their PWM fan from that family to then find a non-HP PWM matching fan.  It is easier to just find the HP part number if present on the fan label, and search for that.  A creative use of this info is if you are sure you want a slower fan than HP chose.... If HP chose the HH one you might search for the MH or M PMW version.  The later HP workstations have not needed such massaging, but I did that on some of the earlier ones.

[SDH]

While we're on the topic of HP workstation fans.... the very best way to see individual fan speeds now is by the workstation version of HP Performance Advisor.... install it, and the answers are in the "sensors" section.  Works well as far back as I tested, to the xw6400.

The free HWMonitor software used to work better but over the years the sensors it probes and dropped off and the fan speed info is not great on HP any more.  HP Performance Advisor seems to get them all, except for the power supply fan in some workstations.

I also use the Noctua 4-wire in line resistor based adapters to drop HP fan speeds as needed for fine tuning.  They have a number of different ones, but the Low Noise Adapter and the Ultra Low Noise Adapter (4-wire PWM version) are the ones I use most, and even double up (in series) two in some cases.  The little southbridge coolers in the xw6600 and the Z600 deserve two of the ULNA in series.

[DGroves]

"SDH"  is correct, the fan itself may be the cause however due to how  hp wires the 2 memory cooling fans using black wires for all of the fan connections it's a bit hard to id the necessary 4 wires to cut when doing a fan replacement (hp just replaces the entire assembly) 

remove the shroud, note the blower fan part number and google it till you find the fan's  family/model series and then read the spec sheet to id the fan connections 

note that the HP fan may have a unique fan model suffix at the end of the fan model if it was made specifically for HP, and that's ok as long as the beginning fan numbers match up           xxxxxx-HP OEM numbers at the end after the "-"

and last, check the shroud's mating pins and do the same for the motherboard to see if one of the pin connections is not making contact

[SDH · Accepted solution]

That cooling unit for the Z820 is complicated, and take a look on eBay for 642166-001.  If you run through them you'll see there is a 5-fan version for Z820s with 1 processor and a 6-fan version for Z820s with two processors.   I'd not hesitate to spend the 35.00-50.00 to get a used one rather than dink with trying to find the blower fan you seem to need as a separate unit.  

[SailorJeffrey]

Thanks all, looks like a new fan assembly is the easiest way to go. Appreciate the assistance.