Convert your 7900GT into a 256Mb 7900GTX

[t024484]

The biggest functional difference between the GT and GTX is that the GTX switches the Vgpu between 1.2 in 2D to 1.4 Volt in 3D.
Thats why the GTX can be clocked at 650 Mhz in 3D.
EVGA has their 7900GT-SS board with increased hardware in the volt mod area, which also enables the switching from 1.2 in 2D to 1.45 in 3D.

My firm believe is, that this voltage switching extends life of your GPU, since most of the time you are working in 2D, and thus you will have the 1.2 Volts on the GPU.
This can be the only reason that I can think of why the 7900GTX as well as the EVGA7900GT-SS have this feature.

I have made the same voltage switching option to a standard 7900GT. This modification can be applied to any standard 7900GT board. You will need a BIOS that switches from VID 0 in 2D to VID 1 when in 3D mode. You can check if your BIOS does this, with the monitor function of Riva Tuner going from 2D to 3D.
You could use the EVGA 7900GT-SS BIOS for this purpose, but you can just as well change your own BIOS with Nibitor, using the advanced voltage editor.
You will also need some soldering skills.

The components that I used, are 2 dual schottky diodes, type BAT54C, and 1 N type Mosfet BSS670S2L, that's all. I bought them from Farnell.com.
Any dual schottky diode with common cathode will do , and any low power N channel Mosfet with less then 10 Ohm channel resistance when switched on is O.K.

The board in the unmodified state looks like:



And after Modification:



Red gives you +0.05 Volt
Yellow gives +0.1 Volt
Purple gives +0.2 Volt

So with the standard 5Kohm resistor giving you 1.2 Volt in 2D, you can now switch to anything between 1.2 and 1.55 Volt in 3D.

If you change to 50 Kohm, you can go anywhere from 1.5 to 1.85 Volt.

Do not bother what Nibitor is telling you what the exact 3D Voltage is, although it should be different from the 2D voltage, with the advanced editor you can give it the value you like. The thing that is important, is that in 3D the GPU switches to VID 1 from VID 0 in 2D.

With these additions, your board is functionaly 100% comparable with a 256Mb GTX.

[sluggo]

That's great, t024484! Now I can get that wire off my board and run coler in 2D. All I need now are a pair of steady hands!

If, instead of using a 5k SMT resisitor I used a dab of conductive paint, would that work or would I end up in a wrong voltage table?

[t024484]

That's great, t024484! Now I can get that wire off my board and run coler in 2D. All I need now are a pair of steady hands!

If, instead of using a 5k SMT resisitor I used a dab of conductive paint, would that work or would I end up in a wrong voltage table?

Intersil specificies a 5Kohm resistor, without telling what tolerance should be.
My experience is that 4k7 is still O.K. , but conductive paint with 0 Ohm is wrong without a doubt. I would say, 5Kohm +/- 10%.

[g_aleph_r]

Sorry double post

[g_aleph_r]

Is dangerous to change the vgpu via dip switch with the pc turned on?
I'll never be able to do this mod!!

[t024484]

Is dangerous to change the vgpu via dip switch with the pc turned on?
I'll never be able to do this mod!!

If you prefer a (dip)switch, I would suggest to switch with the PC turned of.

[alpha0ne]

Thanks t024484

A really easy mod if I can get the parts in AU

[Roger_D25]

t024484,
Do you still want/need that BIOS you asked about? I'd be happy to send it to your e-mail or I'll give you a linky to it over at mvktech as I uploaded it there the other day (Mavke didn't have it). By the way thank you for all the great work and info you give us all! Until I read a few of your last posts I had no idea what those little black components actually where up next to the D508, D511, and Q516 pads were. There responsible for the switching of 2D and 3D GPU voltages, and there called dual schottky diodes, very interesting! Keep it up man, many of us really apprecaite it!

[t024484]

t024484,
Do you still want/need that BIOS you asked about? I'd be happy to send it to your e-mail or I'll give you a linky to it over at mvktech as I uploaded it there the other day (Mavke didn't have it). By the way thank you for all the great work and info you give us all! Until I read a few of your last posts I had no idea what those little black components actually where up next to the D508, D511, and Q516 pads were. There responsible for the switching of 2D and 3D GPU voltages, and there called dual schottky diodes, very interesting! Keep it up man, many of us really apprecaite it!

Thanks you for your offer, but I aready helped myself by visiting MVKTech.
That's how I found out that you can change any 7900GT Bios by means of the Nibitor Voltage Editor, to have two VID levels.
Silly enough, if you could find how to enable the third and the fourth VID level, you could have your EVGA_SS Bios changed to have 1.55Volt instead of the current 1.45 Volt.
All the hardware, read all the little black fellows, are there to do the switching, all you need is the signal from the GPU to get it switched to 1.55 Volt.

[Roger_D25]

Thanks t024484, glad you found it! Which BIOS version are you specifically using, the stock SS one (14.49) of the slightly modified one that came with my card (14.43)? Just curious, I'm pretty sure they are both the same BIOS but with just a few minor changes?

[Z33ky]

Saw this post at eVGA and you'll see in the second post of the string, 2 photos; one before and the other after the return of the 7900GT KO and you'll see that eVGA has done a mod like that shown in this thread.
Card before return:


Card after return:


By the looks of it eVGA has modified the card so that it to has a seperate VGPU for 2D and for 3D. And in a post further down the string by 'saviorself' he posted the following:

"According to Blue Falcon at [H], the cards are now running 1.2v 2D and 1.45v 3D"

What are your thoughts on the matter t024484? Perhaps buying a new 7900GT KO would be a great idea and one wouldn't have to perform the mod described in this thread? Thanks in advance!

[Roger_D25]

Actually it turns out that eVGA has been given out their SS cards as RMA replacments to some of the people who have gone through multiple RMA's with persistant problems. In fact I just recenlty got mine about 2 weeks ago. At first I thought it was just a modified card but it's actually their SS card. Fortuenlty since this last RMA replacment my card has worked longer than any other RMA replacment so far (fingers crossed). I also think this because on my PCB the BIOS version sticker says xxxxx14.49 which is the only offiical SS BIOS version but when you actualy extract my BIOS it's version 14.43 which is a modified version of the SS one with lower clockspeeds to match the cards they replace. I have measured the cards 2D and 3D voltages and they are indeed 1.2v and 1.45 respectivly using a multi-meter.

The only drawback is that even the people getting this SS card as a RMA replacment are having the same problems they had with their old cards? I hope I'm one of the lucky ones!

[t024484]

Saw this post at EVGA Forum. What are your thoughts on the matter t024484? Perhaps buying a new 7900GT KO would be a great idea and one wouldn't have to perform the mod described in this thread? Thanks in advance!

If you buy a new board, it certainly is worth considering to buy an EVGA board with the 1.2/1.45 switching option already installed, like the KO-SS.
On the other hand, the cost of an GTX is "only" 70,- euro more, so this might be an even better option.

But for those already in the possession of a 7900GT, this DIY option that I have described could be interesting to hopefully extending the life of their board. And let's not forget, this is the Xtreme forum.

Somewhat to my surprise, EVGA have added more components than strictly necessary, because it is not only possible to switch to 1.45Volt (VID 1) but also to 1.3Volt (VID 2) and to 1.55Volt (VID 3).
I cannot find the way in BIOS to have VID 2 and VID 3 enabled, so for the time being the extra hardware is partly of use for nobody.

With my modification, I have used the fact that only the VID 1 line is switched, that's why I achieve exactly the same as EVGA, but with reduced hardware.

As a last remark, my guts feeling tells me that it is the 7900 GPU that is very vulnerable, time will learn.
Because of that EVGA is changing their boards to 1.2 Volt in 2D, why would they invest in extra components if it is not necessary.
But although this switching is a step in the direction, I still read of GTX boards and unmodified 7900GT boards that are dying, so it is not the final solution.

In a previous thread I have already mentioned that with the new 90 Nm chip, things are getting more critical than ever.
1 Volt voltage difference into two conductors only 100 Nm apart, means 10.000Volts per millimeter. Enough to fire a spark plug in a car.
The only difference with a spark plug is that it designed to spark, which cannot be said of a GPU chip. So the design of a 90 Nm chip cannot simply be a downgrade of a previous 130 Nm design.

[t024484]

Thanks t024484, glad you found it! Which BIOS version are you specifically using, the stock SS one (14.49) of the slightly modified one that came with my card (14.43)? Just curious, I'm pretty sure they are both the same BIOS but with just a few minor changes?

At the time I am using a 14.47 version from MVKTech.
There are many changes as compared to my original 12.02 version, but I really have no idea what those changes are doing, and wether they are doing something at all.
It seems that the 12.02 version with the added VID 1 switch setting for 3D, performs just as well as the 14.47.

[Augu]

Nice guide t024484 and it worked just fine. In fact i did it to my frend's card becouse he asked me

[Roger_D25]

Thanks again t02448!

[bouc]

really nice, gonna give it a try

[Roger_D25]

bouc are you useing a SS card or just a regular 7900GT?

[bouc]

a regular one (galaxy) why?

edit:
did mod my bios to have two differents vid
looking for components now

[Per Hansson]

The pictures in the first post does not load...

[t024484]

The pictures in the first post does not load...

When I try, everything is there.
If you still cannot see them, let me know and I will send them by mail.

[Per Hansson]

When I try, everything is there.
If you still cannot see them, let me know and I will send them by mail.

I tried with 3 different browsers and also asked a friend that sits on a different ISP and the images did not load... Sure yours are not just cached by the browser?

[bouc]

It's the same for me, no more pictures...

[t024484]

It's the same for me, no more pictures...

I cleared my cache, and the pictures where gone.
so here they are again.
Before Mods



And after modding



Red gives you +0.05 Volt
Yellow gives +0.1 Volt
Purple gives +0.2 Volt

So with the standard 5Kohm resistor giving you 1.2 Volt in 2D, you can now switch to anything between 1.2 and 1.55 Volt in 3D.

If you change to 50 Kohm, you can go anywhere from 1.5 to 1.85 Volt.

Do not bother what Nibitor is telling you what the exact 3D Voltage is, although it should be different from the 2D voltage, with the advanced editor you can give it the value you like. The thing that is important, is that in 3D the GPU switches to VID 1 from VID 0 in 2D.

With these additions, your board is functionaly 100% comparable with a 256Mb GTX.

[***Deimos***]

If you buy a new board, it certainly is worth considering to buy an EVGA board with the 1.2/1.45 switching option already installed, like the KO-SS.
On the other hand, the cost of an GTX is "only" 70,- euro more, so this might be an even better option.

But for those already in the possession of a 7900GT, this DIY option that I have described could be interesting to hopefully extending the life of their board. And let's not forget, this is the Xtreme forum.

Somewhat to my surprise, EVGA have added more components than strictly necessary, because it is not only possible to switch to 1.45Volt (VID 1) but also to 1.3Volt (VID 2) and to 1.55Volt (VID 3).
I cannot find the way in BIOS to have VID 2 and VID 3 enabled, so for the time being the extra hardware is partly of use for nobody.

With my modification, I have used the fact that only the VID 1 line is switched, that's why I achieve exactly the same as EVGA, but with reduced hardware.

As a last remark, my guts feeling tells me that it is the 7900 GPU that is very vulnerable, time will learn.
Because of that EVGA is changing their boards to 1.2 Volt in 2D, why would they invest in extra components if it is not necessary.
But although this switching is a step in the direction, I still read of GTX boards and unmodified 7900GT boards that are dying, so it is not the final solution.

In a previous thread I have already mentioned that with the new 90 Nm chip, things are getting more critical than ever.
1 Volt voltage difference into two conductors only 100 Nm apart, means 10.000Volts per millimeter. Enough to fire a spark plug in a car.
The only difference with a spark plug is that it designed to spark, which cannot be said of a GPU chip. So the design of a 90 Nm chip cannot simply be a downgrade of a previous 130 Nm design.

Amen brother.