7900GT over voltage protection?

**SF3D** · 03-22-2006, 08:33 AM

-DesertShooter-

Could you measure voltage on pin 10. It's important to know which way voltage goes after removing the resistor.

**TimeOut** · 03-22-2006, 08:38 AM

Originally Posted by SF3D

-DesertShooter-

Could you measure voltage on pin 10. It's important to know which way voltage goes after removing the resistor.

It should be the same voltage of pin 4 (VCC). If not, I will have to go back to college and get BSEE again.

**DesertShooter** · 03-22-2006, 08:39 AM

Originally Posted by t024484

How did you increase the Vgpu, 50Kohm to pin 6 or to pin 3.
Did you measure the value of the resistor after having it removed ?

From pin 3, the good way, isn't it?
The resistor has a resistance of 3566Ohm after having it removed.

**DesertShooter** · 03-22-2006, 09:05 AM

The voltage from pin 10 is 1,789v with a 5k resistor, but still no go >1,3v

**t024484** · 03-22-2006, 09:18 AM

Originally Posted by DesertShooter

From pin 3, the good way, isn't it?
The resistor has a resistance of 3566Ohm after having it removed.

Pin 3 is O.K.
The Voltage regulator is definitely not restricting Vgpu, it can only limit the current, but I am beginning to fear that there could be another mechanism there to prevent a higher GPU voltage, that was not there in the 7800GT/7800GTX.

I hate it that I cannot get a 7900GT board myself, it would make life quite a bit easier.
I have a Dell Inspiron 9400 on order with a 7800Go board that cannot be supplied because of problems with the 7800Go, and I have a 7900GT on order that cannot be supplied either.
Is NVIDIA testing how long they can survive without revenue?

**s e t h** · 03-22-2006, 09:34 AM

lets hope there a flood coming after the drought

**t024484** · 03-22-2006, 09:43 AM

I am still studying the ISL6568 for hidden functions, but I also had another Idea.
It could be that the 7900GT checks the applied Vgpu against its BIOS setting.
I know that changing the setting in BIOS does not change the Vgpu, but it could be that if you change the setting in BIOS to 1.4 Volt, it will accept all the sudden a voltage of 1.4 Volt from the Voltage Regulator.
Could anybody try this, it is quite a simple test with NiBiTor 2.8 and NVflash.

I also would like to know what happens to the Vgpu when the screen "turns dark" when aplying a higher voltage than 1.3 volt.
Does the Voltage Regulator keep its voltage or does the voltage get pulled down?

**SF3D** · 03-22-2006, 09:50 AM

After black screen voltage is still same.

***Deimos*** · 03-22-2006, 09:53 AM

good luck guys... we're all cheering you on!

**TimeOut** · 03-22-2006, 10:43 AM

As we can see in some of the 7900 reviews where there are pictures showing the 7900 chips, the 7900GT has a label that explicity states "GT".

My theory now is that nVidia added some voltage sensing and other logic inside the G71 core. Maybe there are bridges on top of the GPU and one sets the maximum voltage allowed. Can we get a close picture of both GT and GTX chips to compare?

Or even worse, maybe nVidia used a laser to cut some bridge inside the core limiting the max voltage to a value < 1.3V .

**Shark-357** · 03-22-2006, 12:28 PM

Here is mine 7900gt ...

**Hugo van Dijk** · 03-22-2006, 01:20 PM

Originally Posted by Shark-357

Here is mine 7900gt ...

As far as I can see there is no diffrence between the GT and GTX

http://www.pcstats.com/articleview.c...id=1930&page=2

**Shark-357** · 03-22-2006, 01:37 PM

Yeah i see so if there are changes they are in the core it self.

**Fhqwhgads6680** · 03-22-2006, 02:10 PM

man why'd nvidia have to do this ?? I was really hoping for a 7900 gtx 256 mb

Well good luck to you guys, I'd be game for attempting some of this stuff...but I don't have the money to replace a dead card.... and my vmoding skills are not the best.... Best of luck tho!

Brandon J

***Deimos*** · 03-22-2006, 03:32 PM

Why?
Thats obvious. nVidia noticed it was too easy with GF4ti4200 and 6800GT. Very simple voltage mods, or just flash bios. nVidia doesnt want folks buying low priced 7900GT because they can easily mod to 7900GTX...

Or, perhaps they noticed websites liek www.xtremesystems.org and wanted to give us a challenge

**t024484** · 03-22-2006, 11:36 PM

Hi guys,
I have some good news.

1) We tried to change the point where the current limit starts, but as it turned out the current limiter is not causing us problems at this moment, but it will surely do if we manage to get the Vgpu higher.

2) We tried to increase the Vgpu by using a pot, because this was always the way to go, BUT NOT IN THIS CASE.
I took a closer look at the voltage regulator, and I found out that changing the output voltage with a pot can BE NO MORE THAN 100mV.
I was not prepared to so much complexity in a voltage regulator, but this one has a real Over Voltage Protection.

The Output Voltage is set digitally, and than turned into an anolog Vref through a Digital to Analog convertor (DAC).
Whenever the output voltage differs more than 100mV from this Vref, the overvoltage kicks in.

The solution to adjust the output voltage is totally simple.
Just change the digital code on the DAC and you are there.

To be able to tell how to go on I need the following info:

1) What is the voltage on pin 1: is it A) below 3Volt, or is it B) connected to +5Volt through a 50Kohm resistor or is it C) connected to +5Volt through a 5Kohm resistor.
2) Now the definition of a digital zero and a digital one for this chip is resp below 0.4 Volt and above 0.8 Volt.
I need to know the digital code on the following pins, exactly in this order:
pin22 pin21 pin30 pin31 pin 32.

I need something like "01110" as an answer.
Pin counting is counterclockwise starting a the little hole in the plastic on one corner.

As soon as I have this info, I can tell what the next step should be.
I have all the confidence that we are heading in the right direction now.

**Pirs** · 03-23-2006, 12:00 AM

nvidia uses usualy VRM9 voltage codes

but I am afraid that change VID logic via hardmod is impossible

(sorry my english)

**GOESA** · 03-23-2006, 01:24 AM

Why don't i have an multimeter with me, it looks like you guys are on the right track GJ and GL getting there, I know a skilled Vmodder here i Denmark, that i would like to do the mod, but it would be nicer if the OVP was gone when i get it modded

/Grau

**t024484** · 03-23-2006, 02:01 AM

Originally Posted by GOESA

Why don't i have an multimeter with me, it looks like you guys are on the right track GJ and GL getting there, I know a skilled Vmodder here i Denmark, that i would like to do the mod, but it would be nicer if the OVP was gone when i get it modded

/Grau

You cannot remove the OVP. But it does not stand in the way if you change he digital code on the DAC.

PIRS thinks that NVIDIA uses the VRM9 code, which should mean that pin1 is connected to +5Volt through a 50Kohm resistor, but of course somebody should check this.

I see no reason why the digital code cannot be changed. It is simply changing a zero to a one or vice versa on the input poins of the Voltage Regulator.

**VoRtAn_MaDgE** · 03-23-2006, 05:24 AM

Nuno.

I contacted the designer and the product line applications engineer about your request. They have NO recommended method for disabling the OVP network as the circuitry is internal.

IF the product line designer for the family of part has not recommended method, then sorry, Intersil does not have any recommended method for disabling OVP.

Answer from an email that i sent to intersil.

**t024484** · 03-23-2006, 05:31 AM

Originally Posted by VoRtAn_MaDgE

Answer from an email that i sent to intersil.

This is exactly what I said in my previous mail, but don't bother, when you change the digital code on the DAC, the OVP shifts with the new setting.
OVP is always 100mV more than the Digital Setting, no matter what the setting is.
Forget the pot, changing Vgpu has to be done digitally from now on.

**SF3D** · 03-23-2006, 06:01 AM

I was thinking this yesterday and did it.

IT WORKS!!!!!!

This is with 1.5V VGPU

Attachment 45098

I will make a picture later, so everyone can do this.

**Clint** · 03-23-2006, 06:08 AM

You better change your sig now then

**SF3D** · 03-23-2006, 06:14 AM

This is how you do it.

Attachment 45100

Enjoy!

**Hugo van Dijk** · 03-23-2006, 06:19 AM

SF3D well done

Now show use some 7900GT POwwa @ 1.5V

Thread: 7900GT over voltage protection?

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