Ensuring the fan runs on my HP ProBook 6450b laptop


I have an HP ProBook 6450b laptop which runs Ubuntu 12.10 and Windows 7. It had a tedious and potentially expensive problem: when running Linux, the CPU fan would fail to turn on until the CPU temperature reached 105℃. This was dangerously hot. I wrote about the problem in detail on the Ubuntu Forum, including links to my conversations on the linux-acpi kernel list.

After spending about a month trying to find a software fix for this problem, I decided it was time to get the soldering iron out to fix the problem. Here's what I did:

  • I followed the official HP guide for removing the keyboard (it's really easy).
  • There are three wires running from the motherboard to the CPU fan:
  • I cut the blue wire and left it disconnected.
  • I cut the red wire and tinkered with different resistors spliced into the red wire. I searched for a fan speed which would be quiet but produce significant cooling:
  • I settled for two resistors in parallel:
  • One resister was a 47Ω (yellow, purple, black) the other was a 470Ω (yellow, purple, brown) giving a final resistance of 42.7Ω.
  • The finished product (not very tidy but it works!).

(disclaimer: I'm not even vaguely qualified to tinker with laptop hardware. I'm just some dude from the internets. I hacked together a solution which worked for me and I've done my best to report what I did in the hopes that this solution might work for others. If you break your laptop trying to follow these steps then I'm sorry but I can't be held responsible.)

Comments

I had been plagued with the same issue for long. 13.10 seems much better in this regard. Also, my CPU temp. shot down to Windows like, after i installed restricted drivers (which i think is always risky). So back to 3 hours of battery life and cooler CPU even in Ubuntu :)

I was struggling with what seemed to be exact symptoms with an Asus eee-pc r051bx. It had a "Critical" temp of 98 deg C, and was reaching that quickly. Sometimes it would start the fan at about 90C, but only for maybe 5 seconds. After that it would just keep climbing until it shutdown. Basically I couldn't get the fan to stay on.

I tried many additions via /etc/grub/default such as acpi_osi=Linux, acpi_backlight=vendor, and acpi_enforce_resources=lax. Nothing worked. I would hear the fan start up with a "puff of air" then immediately stop, but otherwise the fan would not come on and it would just keep the temp climbing until it shutdown, even when not under much of a load.

In a fit of desperation, I tried this addition to the grub line:

acpi_osi=Windows

Even though I had no confidence it would work. However, after rebooting the fan now runs constantly at a slow rate, and temps are hanging at about 63C (this is great considering what it was before). So, in summary, add "acpi_osi=Windows" to the end of the GRUB_CMDLINE_LINUX_DEFAULT line, then save, run "sudo update-grub" and then reboot.

PS this is with Ubuntu 14.04 "Trusty", using the 3.13 kernel. I had previously tried the 3.19 kernel which gave the same (bad) results.

very interesting information, thank you very much!

Hello Jack Kely,

Recently one friend of mine gave me the same laptop as yours (hp probook 6450b). It was broken and i couldn't turn it on. I did some diagnostics and I found a lot of problems. The main problem was a broken hdd. I replaced it and I managed to install Ubuntu 15.10. I saw that i had overheating problem and i opened the case to see whats going wrong (i found that the fan didnt work). After a research on Internet i found a lot of your post in different sites about this problem.
So i deceided to install windows 7 to see if I have the same problem as you. And yeah, it was exactly the same case. In addition, I noticed that the laptop takes a lot of time to turn off.
I upgraded the BIOS and still had the same problem.
After that, I decided to remove the internal battery (of the motherboard) for some minutes and install it again. I reset the factory settings in BIOS and boot again on windows. After that i noticed that i solved somehow the problem that i had when i was trying to turn off my laptop.
Do you have the same problem when you turn off or restart your computer ?

I was curious and i installed again Ubuntu, and I saw that i didnt had any overheating problems.
I was monitoring the temperature with lm-sensors and it didnt went higher than 50 C. However the fan wasnt working.
I played a 1080p video, and when the temperature exceeded the 50C the fan started working ! (after 20min of playback, the temperature didnt exceed 60 C).
I dont know how and why, but maybe its a BIOS problem.
At this time I am trying to upgrade the ram. Whenever I put the new ram the laptop doesnt boot. Hope that i will manage to solve this problem too.

Greetings
Orestis

Hi Orestis. Glad you're making progress with your 6450b! My laptop almost always turns off quickly (from both Ubuntu 15.10 and Windows 7). Best of luck getting your machine to work perfectly...

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