If your fan control on your 3870 does not work, here is how to flash it:

Some files: here

-DON'T USE ATIWINFLASH.exe. Your system will hang. Your card will not work, and you will have to do it with another or integrated video card. Use atiflash.exe

Backup your bios
-use gpu-z to backup your video card bios. Click on bios chip icon near bios version in gpu-z. (save to file, ending in .bin)

Modify your bios
-download program RBE_128. (Radeon bios editor.)
-load bios. Find your .bin file.
-go to fan settings
-click on "set all fan setting to recommended values".
-file/save bios. Save as file, ending in .rom.
-exit program

Flashing your video card
-find and download atiflash_386.zip.
-download boottoolkit from vuks.vdsworld.com.

-Create iso with atiflash.exe and your modified bios file-
-unzip atiflash.zip
-unzip boottoolkit to d:\temp
-copy atiflash.exe to D:\temp\flash\boottoolkit\files (assuming you unzipped boottolkit file to d:\temp)
-rename your saved bios from "2D - 300, 900, 1.134 3D - 825, 900, 1.214.rom" like name to "myfixed.rom". Make sure it has the same ending as the original name, which is .rom.
-copy myfixed.rom to D:\temp\flash\boottoolkit\files.
-delete bootcd.iso file, if it exists, in D:\temp\flash\boottoolkit\.
-Click on make_boot_iso.bat, to create new bootcd.iso.
 (alternative method is to use Ultraiso to modify bootcd.iso from boottollkit package. Atiflash.exe and myfixed.rom should be at the root of the iso file.)

-Flash from dos-
-Burn iso to the cd, or cdrw.
-If you have UPS, connect your PC to it.
-Setup PC, in bios, to boot from cd.
-Boot pc.
-Select "Boot with CD support"
-after booting, type C:, or D: to get to atiflash.exe
-use "dir" to display direcotry content, "cd newdirectory", to change directory
-to flash card type this:
 "atiflash -i" will give you info on ati cards present. First will have id 0, second 1.
  If you have one ati card, it's id is 0
 "atiflash -p 0 myfixed.rom" will flash your adapter with myfixed rom.
 "atiflash -p 0 myfixed.rom -f" will force flash your adapter with myfixed rom. I used this after first unsuccessful flash. Second one was successfull. :)

It is best if you can make flash from your own card. If not try to find one from the same version/manufacturer video card,  and/or the one with the same bios size.

Good luck.



Testing
-You can change video card fan speed and memory speed with Riva tuner. Ati tray tools did not work for me.
-In Riva tuner go to the main tab. Click on the triangle near Customize. Select first icon.
-Go to fan tab.
-Enable low level fan control. set speed to auto and enable "Apply fan settings at Windows startup."
-You can watch fan speed temp with gpu-z.
-You can monitor/test your gpu with with Furmark. Also Gpu-z comes with the same package.


Instal monitor drivers if you get out of sync problem (unrelated to bios flashing.)





Doing it with another video card
Here is how:

I used pci card (really old S3 graphic card. It goes in the same pci slot that separate lan card, modem, or sound card goes,
PCI)

Go to bios of your pc. I used Asus motherboard. In the pci? settings there is an option of which video card you want to initalize first, which pair to use.
I used pci card, and my Ati card was PCIEx So my bios was set PCI/PCiex. PCI is old S3 card, PCiex is new 3870. I could not get video when it was set to integrated/PCIEX. I could see things on monitor, but, atiflash could not find ati adapter.

If you have motherboard with Integrad video card, then you shoud use Integrated/PCIEx order, I suppose.