Upgrading Dell Latitude C640 CPU

Just because it’s quite cheap, via ebay, I decided to upgrade my Dell Latitude C640 CPU from a 2.0 GHz P4-M (SL6FK) to a 2.4 GHz one (SL6VC). It could, in theory, get a 2.6 GHz one, but these (like SL6WZ) are way more expensive.

The Dell Latitude C640 service manual describe in lenghty details how to actually change the CPUs. There isn’t much point in describing it here: just remove the hard drive, the keyboard, then the CPU thermal cooling assembly and you can easily access the CPU socket.

After that change, the BIOS complained about a “Processor Microde Update Failure – The revision of processor in the system is not supported.”, an error message that does not prevent the system from booting succesfully. A quick check with dmidecode showed me the current BIOS was version A08 released 03/04/2003. I decided to upgrade the BIOS too, following these advices. I downloaded a windows BIOS update from dell website.  On a computer with wine available (not the case of my laptop),  I ran wine ./R71684.exe and stopped after it extracted all the files it contained, then I ran unshield x data1.cab to get the contents of this cabinet. I found a file BiosHeader/C640_A10.HDR that I copied on my laptop. On the laptop, with the package libsmbios-bin installed and the module dell_rbu loaded, I ran dellBiosUpdate -f ./C640_A10.HDR -u which returned:

Supported RBU type for this system: (MONOLITHIC)
Using RBU v2 driver. Initializing Driver. 
Setting RBU type in v2 driver to: MONOLITHIC
Prep driver for data load.
Writing RBU data (4096bytes/dot): .................................................................................................................................
Notify driver data is finished.
Activate CMOS bit to notify BIOS that update is ready on next boot.
Update staged sucessfully. BIOS update will occur on next reboot.

Then rebooted the laptop and it restarted mentioning it was now running BIOS version A10. Cpufreq works fine, everything is in order.


3 thoughts on “Upgrading Dell Latitude C640 CPU

  1. Topper says:


    I also have a C640 (actually its Inspiron 4150 clone cross-flashed with c640 A10 BIOS & working great with the c640 accessories, including a C/Dock II modified as described here http://www.bay-wolf.com/Modify-Lat-to-Inspiron.htm) and am considering upgrading the CPU from the 1.7Ghz to the 2.4Ghz such as described in your post as well as RAM to 2GB.

    Wondering if you might be still using the C640 with the upgraded processor and how it might be working out for you – especially as far as heat dissipation goes? Does the laptop get considerably more hot compared to prior to the CPU upgrade or is the cooling mechanism (factory installed heatsink, fan assembly, vent etc) design adequate to keep the new CPU as cool as the original CPU?


    • Hi Topper,

      Yes, I’m still using this laptop everyday. I mainly use it to watch movies in bed and as alarm clock, with KDE desktop.

      I use i8kmon to manage the two fans it has. I configured it so it allows quite high temperatures (as I’m not focused on keeping this hardware for so long) but use the fans as little as possible, the secondary fan being really noisy.

      So far, it’s ok for me. For instance:

      $ sensors
      Adapter: Virtual device
      Case L Fan Speed: 0 RPM
      CPU R Fan Speed: 0 RPM
      CPU Temperature: +62.0°C

      I think it’s acceptable, heat dissipation wise. It’s look to me that the cooling mechanism was design to work properly with 2.4 CPU as well as lower speed CPUs.

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