I'm using Asus 7970 DCU II Top. I can't unlock voltage. I saw many people (gigabyte users, Sapphire users.. ) has the same problem. Anyone has a solution? Afterburner,  Trixx, GPU tweak nothing works?!

Depends on the voltage regulators they used, some are adjustable, some are not. It's not a reference card, so you need to post in the ASUS forums.

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Crosshair IV Formula, Phenom II x4 965 w/ Corsair H60, 8 GiB OCZ Platinum DDR3 1600, XFX HD 7970 Ghz, 512GB Vertex 4, 256GB Vector, 240GB Agility 3, Creative X-Fi Titanium w/ Creative Gigaworks S750, SeaSonic X750, HP ZR2440w, Win 7 Ultimate x64

I did, but there is no solution. Also Gigabyte forums.

If the regulators don't support adjusting the voltage, then you can't adjust the voltage

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Crosshair IV Formula, Phenom II x4 965 w/ Corsair H60, 8 GiB OCZ Platinum DDR3 1600, XFX HD 7970 Ghz, 512GB Vertex 4, 256GB Vector, 240GB Agility 3, Creative X-Fi Titanium w/ Creative Gigaworks S750, SeaSonic X750, HP ZR2440w, Win 7 Ultimate x64

According to Asus, you can use there ASUS GPU Tweak utility to adjust it. If not you need to be talking to asus about a possible RMA, or a possible change during the production cycle that disabled voltage control. 

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