Voltage mod – AMD 6970m

The AMD 6970m is an amazing notebook graphics card, great price / performance ratio and really powerful. Only drawback I can think of is that there’s no way to increase the voltage of the card via the VBIOS. This limits the maximum possible overclock and minimizes the benching capabilities of this card.

To solve this I decided to do some modifications directly at the hardware which allow me to increase and also monitor the core voltage of the GPU

How does it work?

The core voltage of the GPU gets controlled by a PWM regulator made by intersil, the ISL62883C.
It’s a small 40 pin SMT chip, here’s the pin configuration of it:

The exact purpose of each pin is described in the datasheet which you can find easily online.

I won’t go into details about how the chip exactly works, all that is needed for the voltage mod is Pin 12 (VSEN). This is the voltage sensing pin of the PWM controller, it monitors the GPU voltage. As soon as the voltage drops below a certain level (e.g. because there’s suddenly more load on the GPU), the chip will automatically give an additional PWM signal to bring the voltage back to the set level.

So if the voltage at Pin 12 is too low, the voltage gets raised. This means if you trick the chip into thinking the current core voltage is too low (even though it isn’t), it will automatically raise it (and thus overvolt the GPU). This can be achieved by slightly dropping the voltage at VSEN.

The resistance between Pin 12 and ground is about 14Ω, putting a variable resistor between ground Pin 12 will allow lowering the resistance between ground an VSEN and thus lowering the voltage at VSEN. The resulting resistance is R1*R2/(R1+R2),  R1=14Ω,  R2 = potentiometer used for the mod.
A 500Ω potentiometer will do the job, I use a 1kΩ which is fine as well.

So such a mod simply requires:
- a potentiometer between VSEN and Ground
- a measuring point to monitor the GPU core voltage

 

Here you can see the conducting path that leads away from Pin 12 (red), possible solder spots for the mod are marked with green.
The parts are pretty tiny, you’ll need a steady hand and a fine soldering tip if you want to do this. It can be done without a magnifying glass, but it’s good to have one for checking the solder joint afterwards.

 

 

 

 

 

On the right picture you can see the cable which leads to one end of the potentiometer, soldered to the card. Could definitely be better, but it works.

 

 

The other end of the potentiometer needs to be connected with ground. Since ground of the PWM controller isn’t accessible (it’s on the bottom of the chip) I had to look for a different possibility. I decided to go for an easy to solder spot, see the picture. This works fine, it has a big contact surface and to solder on a cable there isn’t difficult.

Such a voltmod requires a possibility to properly monitor the GPU core voltage. You can’t just adjust it without knowing how much it gets changed (unless you want to burn your card). Since this isn’t a desktop system it’s not possible to simply do some measuring with a multimeter while the system is running, you need to solder on a cable to a measuring point for the core voltage.

The easiest possibility is to use one of the big electrolytic capacitors on the top of the card (the positive end obviously). Other possibilities are some of the ceramic capacitors opposite  of the die (which would probably be slightly more accurate). I tried this, but it’s a PITA to solder there and I ended up doing it the easy way.

For ground reference you can simply use the ground cable which is connected with the variable resistor.

Here some more pictures, showing the back of the card and the wires coming from the system. You can see that I also put a thermal pad on the VR. It’ll run warmer than usual with the increased voltage, so this might be help a bit.

 

 

 

 

 

On the other pictures you can see the cables coming from the GPU leaving the system. Black is ground, yellow leads to VSEN and orange is the reference for the GPU core voltage. The picture on the very left shows my voltage control center, it simply consists of a breadboard which connects the ground wire and the vsen wire with the potentiometer and it also makes monitoring the voltage pretty easy.

 

Quickly testing the setup shows that it works fine.  Take a look at the pictures showing GPU-Z and the multimeter display. On the right pic you see the card idling, voltage gets reported as 0.9V, the multimeter confirms this. Then I slightly adjusted the potentiometer, resulting in an increase of the voltage, the GPU is still idling, but the voltage is 0.1V higher than previously.

NOTE:  GPU-Z only reports the value which is written in the VBIOS, not the actual voltage, so you can’t use it for the purpose of monitoring. It’s necessary to have a separate wire leading to a VCC reference point in order to keep an eye on the voltage.

 

Here some screenshots of running 3dMark11 at 900MHz core clock and above, the mod definitely does it’s job. But more voltage always results in much more heat. In case you want to do an extreme overclock you’ll have to think about auxiliary cooling methods.
The 3dMark results may not seem too impressive, the problem is that the Alienware M15x was never designed to handle such a high power draw from the GPU, the voltage supply for the graphics card is simply not sufficient and gets to its limits. That’s also why I didn’t overclock the CPU too, the CPU can leech power from the GPU.
Nevertheless, a GPU score of almost 4200 has never been seen on a 6970m in the M15x, this definitely demonstrates the capabilites of  such a mod.

A more recent and more powerful system, like an M17x r3 should be able to handle this modification better. Testing this in an R3 is planned and as soon as there are results I’ll update this article.

If you have a question feel free to leave a comment or contact me at the forum.