Nvidia 8800GTS Vmods

Your card is a monster bro, im envious :). Get it vgpu modded and let it really shine. If you paired that GTS with a Q6600 you would be looking at 15000+ in 3DMark06.

Hi what is max volt for GPU,I set my 1.42v and result is :716/1782/2416
13526 :http://service.futuremark.com/compare?3dm06=3915157

Nice clocks, especially the ram. Max volts imo depends on your cooling, its really limited by temperature, until you reach the OVP level which is usually encountered after setting 1.44 - 1.45v idle. If you did the OVP mod too, perhaps up to 1.5v would be ok, as imo the PWM on the card would be reaching its limit between 1.5 & 1.7v. I'd recommend the HIPRO5 coil & cap mod if you want to go over ~1.6v

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Originally Posted by Timbosan

If you did the OVP mod too, perhaps up to 1.5v would be ok, as imo the PWM on the card would be reaching its limit between 1.5 & 1.7v. I'd recommend the HIPRO5 coil & cap mod if you want to go over ~1.6v

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Originally Posted by SuAsDu

Is there a way to disable ovp on these cards?
SAD

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Yeah, the OCP mod (from here) is NOT the OCP, it's OVP mod actually. It based on replacing (lower) the resistor, connected to Vmax pin of the PX-3540 (pin#41), but... The problem is, that with 8800GTS the OCP works earlier, than the OVP, so this mod can't help. But... :)
As we know, the 8800GTS has 3-phase power conversion, so there are 3 resistors, that used for OCP (1 resistor at each phase). If we remove them, the OCP will disabled permanently. It'a a pity, that there is no exact pinout for the PX-3540 chip till now, so we can only guess:

http://images.people.overclockers.ru/preview/141832.jpg

The red marked resistors shoud be in the OCP scheme, but i'm not 100% sure of it. Why Shamino keeps silence? I appreciate any help :rolleyes:

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Originally Posted by Timbosan

Nice clocks, especially the ram. Max volts imo depends on your cooling, its really limited by temperature, until you reach the OVP level which is usually encountered after setting 1.44 - 1.45v idle. If you did the OVP mod too, perhaps up to 1.5v would be ok, as imo the PWM on the card would be reaching its limit between 1.5 & 1.7v. I'd recommend the HIPRO5 coil & cap mod if you want to go over ~1.6v

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But I use stock cooler,and I think 1.5 is dengeros volt for air cooling.
Sory for my engl.

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Originally Posted by N1ck R1mer

Yeah, the OCP mod (from here) is NOT the OCP, it's OVP mod actually. It based on replacing (lower) the resistor, connected to Vmax pin of the PX-3540 (pin#41), but... The problem is, that with 8800GTS the OCP works earlier, than the OVP, so this mod can't help. But... :)
As we know, the 8800GTS has 3-phase power conversion, so there are 3 resistors, that used for OCP (1 resistor at each phase). If we remove them, the OCP will disabled permanently. It'a a pity, that there is no exact pinout for the PX-3540 chip till now, so we can only guess:

http://images.people.overclockers.ru/preview/141832.jpg

The red marked resistors shoud be in the OCP scheme, but i'm not 100% sure of it. Why Shamino keeps silence? I appreciate any help :rolleyes:

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Read: http://forums.vr-zone.com/showthread...=189621&page=2

Didn't get to try it myself. Still got the GTS arround, but I gave up since my last few benchmarks runs. Try adding the chokes first though.

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Originally Posted by wittekakker

Read: http://forums.vr-zone.com/showthread...=189621&page=2
Didn't get to try it myself. Still got the GTS arround, but I gave up since my last few benchmarks runs. Try adding the chokes first though.

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Hmmm... Shamino says:

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what u need for ocp is to remove 3 resistors / 4 resistors for gts/gtx and it wil nvr sense too high a current

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So, as I see, we have the same theory :rolleyes: But Shamino didn't say definetly which resistors he had in view of OCP Mod :( Could you please ask him at that vr-zone.com-thread about the OCP resistors? I can't post anything there ("avaiting activation" for about a week after I registered :shrug: ).

P.S. I've added 3 Low-ESR capacitors 1500 mFx6,3V (Hipro mod), it helps, but still not enougth to get 702/1620 MHz stable. 1.45 V helps, but the OCP spoils it all.
P.P.S. I'm using the Thermalright HR-03 Plus VGA cooler with my Leadtek 8800GTS card.

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Originally Posted by N1ck R1mer

Hmmm... Shamino says:



So, as I see, we have the same theory :rolleyes: But Shamino didn't say definetly which resistors he had in view of OCP Mod :( Could you please ask him at that vr-zone.com-thread about the OCP resistors? I can't post anything there ("avaiting activation" for about a week after I registered :shrug: ).

P.S. I've added 3 Low-ESR capacitors 1500 mFx6,3V (Hipro mod), it helps, but still not enougth to get 702/1620 MHz stable. 1.45 V helps, but the OCP spoils it all.
P.P.S. I'm using the Thermalright HR-03 Plus VGA cooler with my Leadtek 8800GTS card.

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Very same way I tested my card, but like I said, you should first try the choike modification because it has allready been confirmed as working. Second, I don't think Shamino has a GTS around, but as far as I can see, adding resistor over the caps I've showed might also work out. I don't know what value you'll need, try variable resistors instead.

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Originally Posted by wittekakker

Very same way I tested my card, but like I said, you should first try the choike modification because it has allready been confirmed as working.

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Adding parallel chokes is nonsense, the total inductance of 2 parallel chokes are lower and HF voltage spikes just growing. This is the basics of elecronics - I've no idea why Hipro posts this - the only effect of such mod is appreciable reduced filtering. If we remove regular chokes and replace it with tne new ones - it could work, but:

- the power converter uses very-high frequencies, so the new chokes must have HF-ferrite core, otherwise it will heat up very-very-very fast and even could damage the whole card. I have much experience of replacing chokes at the Palit 7900GS and I know what I'm talking about, it's very hard to find suitable ferrites :mad:
- you need an oscillograph to estimate the effect of such mod's, or we can't determine was it good or bad for the card.
- the new case-free chokes will whistle at every scroll step in IE and this is really annoying.

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Originally Posted by wittekakker

Second, I don't think Shamino has a GTS around, but as far as I can see, adding resistor over the caps I've showed might also work out. I don't know what value you'll need, try variable resistors instead.

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He said about "3-resistor-removing" at GTS - maybe he knew what EXACTLY these resistors are? :help:

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Originally Posted by N1ck R1mer

Adding parallel chokes is nonsense, the total inductance of 2 parallel chokes are lower and HF voltage spikes just growing. This is the basics of elecronics - I've no idea why Hipro posts this - the only effect of such mod is appreciable reduced filtering.

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With choikes in parallel, the total amount of current running through each choike is devided over each parallel choike, meaning that less voltage will drop per choike, meaning that the Vdroop will decrease too because. Inductance decreases, thus less filtering, atleast that is what I think about it.

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Originally Posted by wittekakker

With choikes in parallel, the total amount of current running through each choike is devided over each parallel choike, meaning that less voltage will drop per choike,

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Right, this is the basics - parallel conductors connection.

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Originally Posted by wittekakker

meaning that the Vdroop will decrease too

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No, there is no noticeable decrease of the Vdroop even if we shortcut all three chokes becase of the low choke resistance (they already have too small inductance for that). What we can do - is to make some kind of feedback to Vsenp pin. But my task #1 is to disable OCP.

Well, the resistors next the those caps are part of the current sensing circuit, you could always get rid of them and see what happens.

in that thread, someone already asked him about the resistors but about 2 weeks after he had posted so he probably never saw it. Im a member there so i have PM'd him asking which resistors if he knew, so if he gets back to me ill let you know what he says.

So, I've removed these 3 resistors at last :)

http://img145.imageshack.us/img145/4...0096bv5.th.jpg

The effect was pretty unexpected:

1. Vpgu raised (about 0,1 V higher).
2. There is NO MORE Vdroop, the voltages in 2D and 3D modes are the same!
3. The OCP stayed where it was, but there is no more blank screens - the PC just shuts down immediately when the OCP works.

P.S. So, now 8800GTS voltmode can be executed in such simple way - remove these 3 resistors, Vgpu will be about 1,37 V w/o any Vdroop!
If you have any comments - please welcome.

wow thats my kind of mod :D

ggod work n1ck. so the OCP must work through other components - just need to find them! do the pads where you unsoldered have continuity with these SMC's? (see pic) maybe removing them may do it?

btw shamino hasnt got back to me yet.

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Originally Posted by Timbosan

ggod work n1ck. so the OCP must work through other components - just need to find them! do the pads where you unsoldered have continuity with these SMC's? (see pic) maybe removing them may do it?

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Yeah, they have - just look on the previous photo:

http://images.people.overclockers.ru/141832.jpg

Maybe I should try this, but the competent Shamino's advice would be certainly better.
I'm still not determined about it :confused:

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Originally Posted by Timbosan

btw shamino hasnt got back to me yet.

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Maybe he's on a vacation? :shrug:

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Originally Posted by N1ck R1mer

Yeah, they have. Maybe I should try this, but the competent Shamino's advice would be certainly better.
I'm still not determined about it :confused:

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he may be away im not sure. im not home now if i was id do it but is there 3 resistors with one side having continuity with the pins i have marked on the pic? from the data sheet for px3535 these are ISEN pins 1, 2 & 3 (i think the only relevant ones for us due to the 3 phase power) and appear directly connected to resistors called RSEN 1 to 3 (I think these are the ones shamino was thinking of).
but i also read that the trigger for the OCP is a change of capacitance across the caps (rather than the resistors) in the current sense circuit, which is why i suggested removing the caps.

im also confused wish i was home with my dmm :shrug:

edit: pic removed (see pic in next post) - sorry

Please edit your msg, the pic is very large :eek:

http://img473.imageshack.us/img473/6...8356gv5.th.gif

I think the px3535 pinout is totally mismatch with our px3540. The left red dot on the pic seems not connected with these resistors, but for sure i have to measure it.

Considering I will never have the time to finish my studies, here is the infp I've collected few weeks back:

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Originally Posted by geoffrey

Introduction
During my research for higher performance I've come across many different electronic schematics. Most of you know the existence of usual voltage mods and current protection tricks, let me tell you that for the NVIDIA 8800GTS we are having quite a hard time finding out what is holding back our overvolted cards. From what it seems, a over current protection kicks in whenever the GPU is heavy loaded (i.e. when high current is flowing through the GPU). The screen freezes and the PWM voltage module reads 0V. In order to know how we can fix this we must first understand how the PWM module exactly works and how the current sense network can be modified. For GeForce 8800 cards NVIDIA has chosen for the Primarion PX3540 PWM controller, here is a small schematic:

http://www.xtremesystems.org/forums/...1&d=1196874216

For most people this won't look very clear, but let me tell you that this controller isn't that much different compared to many others I've seen, it only has more options and more PWM phases... Let's us first have a talk about how this type of voltage converter actually works.

+12V

Modern PC's have 3 common voltage levels available which feed most of its components, 3.3 Volt, 5 Volt and 12 Volt. Back in the old days the 3,3 and 5V line were used to feed the processors and DRAM modules, though over time the power usage of some modules become so high that is was in fact more attractive to use the 12V line as feed for CPU's and GPU's, it is much easier to supply high power at those voltage levels. Though, 12V is far beyond the maximum supply voltage for the high switching transistors found in modern microprocessors, therefore we needed a circuit which converted the 12V DC voltage coming from the PSU into the 1,5 Volt which is needed to feed the CPU. Such circuits are called DC-DC converters because they convert a certain DC voltage into a lower level DC voltage. Have a look at the following picture:

http://www.xtremesystems.org/forums/...1&d=1196874216

The above picture shows a 12V DC power supply, a switch, a coil, a diode and a certain load which could be a lamp for example. The lamp will only light up whenever the switch is closed, that makes perfect sense to anyone. Now, if we rapidly set the switch to open and closes states, then the lamp will light on/off too, and if the on time is on par with the off time then the average voltage would be 12/2= 6 volt. If we would measure the voltage over the lamp we would see a square wave, something like this:

_|-|_|-|_|-|_

Now, in order to no longer switch on/off the lamp you could add a powerful coil in line with the lamp. Properties of coils tells us that they will work against the current flowing through them, therefore you will get a sawtooth kind of current flowing through your lamp, it will no longer have to switch on/off, we have created a kind of DC voltage though there is still lot of AC characteristic inside it. If you use your scope you will see something like this over you lamp:

/\/\/\/\/\/\

What the above picture doesn't show is the capacitors which are needed to filter the ripple out. After the coil one should add few capacitors, depending on their size the voltage measured over the lamp will become more or less a stable 6V voltage line. The caps aren't placed in line with the lamp but rather placed over the lamp, in parallel if that is easier to understand. You now will now have decent supply voltage which also could be used to feed CPU's, DRAM modules, ...
In real life that switch isn't set on/off twice a second, but rather few hundred thousand times per second. We won't dive further into the whys here, you must only know that for this rapid switch we can't use human power to make the switch flip levels, nobody is that fast. We could use mechanical switches like a relais, though mechanical switches tend to have a very limited life cycle, after a month a relais could be burned for example. Mosfets on the other hand can be turned on/off almost unendless and are perfect for such operations, in computers we find N-type mosfets to switch the 12V line on and off.


GPU nominal supply voltage

In the above example we successfully converted 12V DC into 6V DC, but how can we build a DC-DC converter which is capable of delivering 1,5V on it's output? It's all in the name in fact... PWM, Pulse Width Modulation. With this technique we are going to change the on and off times of the switch/mosfet.
In our above example we've switched the mosfet on for 0,5s, and switched it back of for 0,5s. The total wave length would be 1s, and the on state would be 50% of that total wave length, we speak of a duty cycle of 50%. Now, if we change the duty cycle to only 25%, then the mosfet would be switched off for 75%, and the average voltage would be only 25% of 12V -> 3V. If you understand well, the duty cycle defines the output voltage, the lower the duty cycle, the lower the average voltage, and the lesser light your lamp will create.

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Originally Posted by geoffrey

PWM modules explained

To give you an idea of current PWM modules I've added a simplified connectivity drawing of the NX2415 PWM controller:

http://www.xtremesystems.org/forums/...1&d=1196874216

You can see the 12V line coming from you PSU at the top right of the picture above. This voltage feeds dual mosfets who will do their own switching algorithm. If mosfet 1 is "on" then mosfet 2 will be "off" and so on. The mosfet have a special connection pin called the 'gate'. Applying a voltage at that gate will make the mosfet more or less resistance free, it will let the 12V voltage through. The pins on the PX2415 controller are therefore called gate drivers in most cases, because they will actually drive the mosfets on and off. Again you can see the coil which creates a sawtooth like voltage line which is being further rectified to a usable output voltage via big capacitors.
In order to check whether or not the output voltage is good, each controller has a feedback loop which compares the circuit its output voltage against an internal set voltage. We won't dive any further into this, my main goal today was to focus on the over current protection circuit. New current sensing techniques learned us to add a RC-circuit (R from resistor, C from capacitor) parallel over the power coil, in this construction the voltage over the capacitor will increase in a linear way with the current flowing through the inductor. If we read this voltage back into our controller this means that we are actually reading in the amount of current flowing through our power circuit. Now look at the lower left side of the controller schematics... You'll notice a resistor divider which task is to set a certain voltage level at the OCP pin of the NX2415 controller. A resistor divider works as following: when you have a 5V DC supply, and you connect two 1k Ohm resistors in series between the + and - connectors of that supply, then you will get around 2,5V in between the resistors and ground. Depending on the size of those resistor, you will measure more or less voltage at that same point. If the first one has a resistance of 2k Ohm instead of 1k Ohm, then you will read less voltage in between the resistors and ground because more voltage has 'dropped' over the first resistor.

http://www.physics.udel.edu/~nowak/p...s/image002.jpg

That's how it works, this way we can change the reference voltage created inside controller to anything useful worth comparing with.

Over current protection

Like I said, the voltage over the Capacitor of the RC network is being read into the controller, inside the controller this signal is compared with the voltage level which we made at the OCP pin. The higher the current flowing through the inductor, the higher the voltage over the sensing capacitor (Cs), and the closer Cs will come to the voltage level applied at OCP, the over current trip point. After OCP has been tripped the controller will shutdown itself in order to protect itself against any damage and your pc will most likely freeze or reboot. We can work around this be changing the resistor values at the OCP pin, though we don't have any specific details about pin connections and functionality with the Primarion PX3540 PWM controller, we are forced to find out how the RC-network works so that we can manipulate the signal that is being read by the controller.

More later on ;-)

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That's why I think that putting a resistor over the SMD caps will influence the OCP trip point. But like I said, no time to really dive into this again, hope someone tries this one out though.

good work putting all that together. its just made so difficult by not having access to the data sheet.

Yes by soldering resistors over the caps we could reduce the voltage signal (used as a current measure) the px3540 see's, and therefore raise the OCP trip point. In the pic ive marked the caps i think we need. You agree? (i know the design of the rc network for the px3540 here will be different & have one more phase to on our cards but just in theory). They are the only resistors connected to the coil & cap for each phase in the diagram.

Now who has the balls to do this mod :)

*looks at card*

sack...........shrinking :p:

not sure enough to do it yet i need to do some more probing with my dmm.

*if* i do this, im thinking 500k ohm VR's across the caps. will do some more measuring & calculations.

also need to sort out my (ridiculously ineffective) stock cooling before i up the vgpu any more i hit 88*C gaming last night.

I found soldering is too risky and require a lot of skill, can I use "conductive glue" as replacement?

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Originally Posted by denden

I found soldering is too risky and require a lot of skill, can I use "conductive glue" as replacement?

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My soldering skills are not great either, I use this 'conductive paint' method instead. >here<

Hope it helps :)