L400 BIOS downgrade solves temperature sensor and fan control issues!

Ladies and gents it’s true:  downgrading the bios from A09 or A08 to A06 solves the fan control issue and restores temperature sensor functionality (ie ACPI works again)!

What does it mean? The L400 can behave as it was supposed to: turn on the fan when it’s hot and turn off the fan when it’s cool enough. No more constant running, horrible horrible fan noise! Also the temperature sensor gives more or less proper readings to for example Speedfan ; temperature (at 700MHz) varies around 48-55 deg. C, around 40-45 at 500MHz.

To check your BIOS version: start the computer and press F2 to enter bios where it shows the version.

To downgrade: download L400A06.exe from Dell’s FTP: Run it and follow the instructions to create a floppy disk and reboot the L400 with it inserted. Follow instructions. After it says it’s complete and leaves you in A:, type l400-a06 /forcemode. It shows a progress window and after a while it reboots and the bios is now downgraded to version A06. Remove the floppy otherwise it will just boot from it again.

Up or downgrading the the BIOS is done at your own risk! Always use AC power (not just battery) when up or downgrading the bios.

The effects of these restored functions on the choice of fan remains to be determined. The 40mm I mounted in an earlier post is a 2-wire fan while the stock is a 3-wire with pwm (speed control).

Edit: The downgraded L400 can start and stop the fan as it should even when using a 2-wire fan. Yay! For those on the lookout for a 3-wire replacement fan I came close to buying a Revoltec airguard 40mm (40x40x10). It should be fairly easy to modify to fit in the L400. The 2-wire fan I use is a Revoltec, part of a chipset-cooling kit.

Edit 2:  March ’09 … Just thought I’d say that the only reason I haven’t posted for quite a while is that with the BIOS finally working (A06)  and a silent fan installed – the L400 is humming along as it should.  Doesn’t really make for an exciting new post if you know what I mean . Anyway, I hope you’ll find something useful here, cheers!