I have Radeon HD4290 onboard and Radeon HD6850 in PCI-E slot.
Onboard card is sufficient for most use cases, but occasionally I'd like to turn on HD6850 to play a modern game.
But even if the HD6850 is switched off in Windows 7 64-bit by disabling associated display its fan still runs, only slower.
Is there a way to make the HD6850 fan run only when I'm using the card?
Simple answer - No. Not without some 3rd party software/hardware.
The fan is probably hooked upto a header on the card which draws power directly from the PCI-E slot, it's 'idle' (slower) speed is a default voltage. Increased load/use (& fanspeed) is controllable, but to actually turn it off would probably involve turning off the PCI-E slots power (which isn't possible).
Easiest solution would be a different fan solution requiring power from a header you can control (ie from the PSU - just use an in-line switch or fanbus).
Just be aware that even with the card disabled/not in use, it is probably still receiving voltage and there is a possibilty of damaging the card if there is zero cooling - ie passive is not enough.
