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limfangjie

1 Rookie

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4 Posts

308

September 4th, 2024 12:16

Dell R740 Erratic Fan Speed on a Single Fan

Hello all!

I'm experiencing a very weird issue with 1 of the 3 Dell R740s we have in our rack.  The fan in the fifth slot seems to ramp up and down very erratically while the speeds of other fans stay constant. This behaviour can get rather annoying as the servers are located in our office and the frequent changes in pitch are very noticeable. The screenshot below shows iDRAC reporting that fan 5 is running at 17000+ RPM while the other fans are running at 7000+ RPM even though the PWM values of all fans are at 37%.

I have tried the following troubleshooting steps:

  • Swap the fan in slot 5 with other fans in the system
  • Swap the fan in slot 5 with a replacement fan
  • Change the thermal optimisation profiles
  • Change the fan speed offsets
  • Change the minimum fan speeds
  • Update the server with the latest firmware and drivers via iDRAC

However, the problem still persists. I thought the operating system may be causing this behaviour but this behaviour also exists whilst sitting in the lifecycle controller. The other 2 Dell R740s have very similar hardware configurations and do not exhibit this issue. May I ask if anyone has any insights on what may be causing this problem? Thank you!

DELL-Young E

Moderator

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5.1K Posts

February 10th, 2025 09:03

Hello, @limfangjie
you can open the case and provide TSR from all problematic servers for deep analysis:
https://dell.to/3CVnuml
TSR logs can explain why fan is running at the high speed -could be configuration, could be 3rd party card etc...
 
Your inlet temperature 27 and 29 is on the high side, should be usually DC is 18-20.
But you do have the server in the office. Rack servers are not designed to be used in the office, usually for office tower servers will be recommended-rack servers may get very noisy depending on the inlet temperature, configuration or production load.

from the screenshot you showed, it's odd: Because you cannot have same p/n fan with 37% PWD running a different speed. So it would be interesting to know if all 6 fans have a same p/n. We request this as well. https://dell.to/40Sg4IB

Respectfully,

DELL-Chris H

Moderator

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9.4K Posts

September 4th, 2024 16:29

Limfangjie,

 

It looks like you have done a lot of the troubleshooting that is needed. With the server still presenting the issue after having been moved, swapped with a replacement, as well as the server being up to date. However, since the issue still persists, it is possible that the problem lies with the fan slot itself.

 

In order to further isolate the issue, you can try swapping out the board from one of your other R740 servers and observe if the problem continues. If the issue does not occur after replacing the board, then it would indicate that the faulty fan slot is causing the problem. In such a case, the recommended solution would be to replace the board.

 

Let me know what you see.

 

limfangjie

1 Rookie

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4 Posts

January 27th, 2025 16:54

Hello all,

I would like to follow up on this fan issue with the Dell R740. As suggested by Chris, I replaced the motherboard on the problematic server back in September as the constant changes in pitch caused by the erratic fan were too unbearable for me and my colleagues. After replacing the board, the problematic server has been working fine ever since. However, a different R740 in another rack has begun exhibiting the exact same issue. The fan in the first slot seems to ramp up and down very erratically while the speeds of other fans stay constant. The screenshot below shows iDRAC reporting that fan 5 is running at 18000+ RPM while the other fans are running around 7000 RPM even though the PWM values of all fans are at 37%.

I have tried to perform the same troubleshooting steps but the problem still persists. Since this has happened to a different server which is connected to a different UPS, I believe that it is not an isolated issue. If anyone can shed some light on why this is happening, I will greatly appreciate the help.

DELL-Charles R

Moderator

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4.4K Posts

January 27th, 2025 18:29

Hello,

 

I see you have done a lot of troubleshooting already. I'd like to see if your tried these steps and the results:

 

*Has any hardware been added or removed from original configuration?

Are there any non-Dell parts?

 

*Are BIOS and iDRAC firmware is up to date?

 

*try Swap Fan1 with another fan. (the image attached shows Fan1 at 18480 RPM)

-check the fan sockets for any bent pins

 

*Check the logs for any entries about fan issues

 

*Run the built in hardware diagnostics in the LifeCycle Controller <F10> run diagnostics

 

 

*Test in Minimum to post configuration to see if the issue persist. If fan speed is ok then add components back a little at a time until you find faulting component.

 

Minimum configuration to POST:

● One processor (CPU) in socket processor 1

● One memory module (DIMM) in socket A1

● One power supply unit

● Right control panel and cable (for power button functionality)

● System board

 

limfangjie

1 Rookie

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4 Posts

January 28th, 2025 02:29

Hello, 

With regard to your questions,

  • Yes, we have added some RAM and a NIC to the server. All of the additional parts are Dell parts except for a USB drive that we use to boot the hypervisor. However, removing the additional components added afterwards does not resolve the issue.
  • Yes, all firmwares have been updated to their latest versions using iDRAC > Maintenance > System Update.
  • The issue still persists with fan slot one after swapping the fan connected to slot 1 with another fan in the server and a new spare fan we keep on hand. The fan that was originally connected to slot 1 does not exhibit this erratic behaviour when connected to any other slots. The pins in fan slot 1 do not seem to be bent.
  • The lifecycle log and system event log did not indicate anything out of the ordinary nor did it mention anything specific about the fans.
  • The server passes all tests performed by the built-in hardware diagnostics.
  • I have tested the server using the minimum configuration to POST by using one CPU, one DIMM, and one PSU. I have also tested it by swapping the CPU with a different CPU we have on hand, changing the DIMMs and replacing the PSU. However, none of these troubleshooting steps has resolved the issue. One thing I've noticed is that the erratic changes in fan speed occur regardless of the state of the server (i.e., it happens when it's booting, sitting in the lifecycle controller, sitting in the hypervisor with the VMs powered off etc.).

Thank you for taking the time to respond to my enquiries.

DELL-Charles R

Moderator

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4.4K Posts

January 28th, 2025 13:38

Hello,

 

Thank you for the reply. Looks like the system board (fan socket) is bad if you swapped fans and the issue stayed in the slot 1.

limfangjie

1 Rookie

 • 

4 Posts

February 8th, 2025 02:04

Hello all,

I would like to follow up on this fan issue with the Dell R740. I've powered off the problematic server and disconnected it from the UPS before the extended holidays and it sat in this state for about a week. After returning to the office today, I powered it back on and noticed that the problem has seemingly migrated itself from fan 1 to fan 6. The screenshot below shows iDRAC reporting that fan 6 is now running at 18000+ RPM while the other fans are running around 7000 RPM even though the PWM values of all fans are at 37%.

Therefore, I now believe that this is not an issue with fan slot 1 itself as fan 1 is now working normally and fan 6 is now erratic. I would also like to reiterate that this erratic fan behaviour has occurred on two separate servers connected to two different UPSes in different parts of the office. I'm not sure how to make sense of this situation so any input is welcomed!

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