Voltage modifications

** NOTE: Madshrimps is not responsible for any damage to your video card. Voltage modifications ALWAYS carry a risk; if you don't want to take the risk, don't do the modifications **

This wouldn't be Madshrimps if we didn't have a look at the possibilities for increasing the voltage beyond manufacturer's guaranteed values. Quite quickly after removing the backplane from the video card we noticed two voltage regulators: the uP6208 and uP6205.



To figure out the Vgpu modification you don't need to be a rocket scientist as it's a plain 'n' simple FB to GND, which is indicated on the picture below:



Sadly enough, as always, it just looks too simple to be true. And in fact it is: although the voltage can be changed quite easily with this modification, you will run into an OVP, or Over Voltage Protection, very fast. To quote the datasheet:

The over voltage protection monitors the output voltage via the Vout pin. Once Vout exceeds Veap + 150mV, OVP is triggered and latched. The uP6208 will try to turn on low side MOSFET and turn off high side MOSFET to protect CPU. A 20uS delay is used in OVP detection circuit to prevent false trigger. Only re-start up can release OVP latch.

So, in order to increase the Vgpu more than 150mV we need to remove the OVP and although it's not that difficult, we'd like you to get to know a different way to modify the Vgpu voltage. This PWM control IC features next to the OVP also an I2C bus, which basically is an interface to communicate with the IC through software. With this I2C feature it's possible for manufacturers, or end-users, to create software to change certain characteristics of the IC, for instance: the voltage. Next to the I2C bus, there's also the possibility to work with VID voltage selection. There are 8 VID pins present on the voltage IC and internally a VID table is stored; the 8 pins can either be turned ON (1) or OFF (0) and each combination of 8 VID pins is attached to a certain voltage. In total there are 256 combinations possible (8 places, 2 options = 2^8 combinations), all of which are described in the datasheet linked above.

As for the application of this I2C feature. I'm not really a very good software programmer, but I was lucky enough that Snot_Aap, a Dutch overclocker, had already programmed this application for the MSI Lightning GTX260, which was used at MSI's MOA EU 2009 final in Munich, which has been covered by Madshrimps not so long ago. All I had to do was check and partially re-write the code to make it work for the Asus Matrix GTX285!



Link (right-click and save): MadMatrix.rar

How to use

Place the 'Madmatrix.bat' file in your rivatuner folder.

Double-click the 'Madmatrix.bat' and enter the HEX value matching the prefered voltage(*)

Make sure you typed the right HEX value and enter 'Y' or 'yes' and press enter.

Check the commands that will be run and press enter.

Check the voltage with a multimeter on the card or with the Asus software utility(*²)

(*): The voltages stated in the utility are not the only ones you can use. As said before, there are 256 combinations, so you will have a look in the datasheet (P.15) if you want to apply a different voltage. Note that the voltage has to be indicated by it's HEX value, so you will need a BIN to HEX converter to translate VID table. Also note that this is a workaround for the OVP problem: by using the software utility, you will not trigger the OVP. OCP, Over Current Protection, still is an issue though.

(*²): This software has compatibility problems with the Asus software as both re-write the VID settings. Please, do NOT use the Asus utility to change ANYTHING (frequency, voltage or fan speed) if you're using the Madshrimps utility. If you use our utility first and then apply anything in the Asus utility, your voltage selection will have been reset!

Next to the Vgpu , we also have the memory voltage to be increased. Again, the modification is in fact quite simple:



At stock settings, the voltage is set to 2.15V, which is enough to do 1400MHz. By increasing the voltage, however, you can get your core and shader frequency a bit more stable.

For readouts, check the picture underneath:



Some small show-offs

As we tested the modifications ourselves, we also had a very quick look at the overclocking capabilities with increase voltage. Here are some screenshots.


(Click to enlarge)

Yes! We were able to bench this card up to 1584MHz (3168MHz real!!) in a 3DMark01 Nature subtest which might as well be a world record as it's the highest benchable memory frequency we've ever seen! Note that this has been achieved on STOCK air cooling and that we're absolutely limited by the temperature, so we are pretty confident that with a bit of extreme cooling (read: liquid nitrogen) 1600MHz benchmark stable should be doable. Of course, when increasing the core and shader frequency, we will have to drop the memory frequency to get the card stable; this test was only to see how far we could get this card scaling.


(Click to enlarge)

The card was perfectly stable at 771/1656/1500. No artifacts, no freezing.