Sapphire 7970 no fans problem

Hi.

I am wondering if any GPU experts can help. I think I did something to my card using a dodgey PCI riser (since replaced with beautiful usb ones. I am pretty upset that I seem to have broken the fans on 1 of my Sapphire 7970s though - and its not the fans theselves as i've connected the fans another Sapphire 7970 which is exactly the same and the fans do work. It is something to do with the actual sensor or power to the fans I believe. In cgminer it says a percentage eg 100% instead of the RPM. Does anyone know if there is any possible fix? The card itself is working perfectly otherwise (755KH/s)- Im using another clip fan to cool it.

Things i've debugged:

I've reconnected the fan plug - no joy.
The fans work when connected to another 7970
Theres no visible sign of damage.

Edit after a reply: I've tried the card directly on the board without a riser.

Is there anyway to test voltage from the 4 pin fan connector with multimeter?

Any help or advise is greatly appreciated.

Thanks.

Check the fan header with a multimeter, yes.

Thanks for reply EarthDog.

Are you able to give me an idea on how to do this with the multimeter

eg,

1) what settings I put the multimeter onto
2) Which probe do I put where

What reading am I looking for?

Thank you.