gf6600 undervolting possible?

[sky]

hi guys..

i need some help here. just rebuilt a sever-esque system running an asus 6600 topsilent gfx card. that's the passive one with the gpu, ram and obviously heatsink on the backside of the card. i've used a 1/2 he pcie riser to fit into a rather flat case (to be finished yet). this mother is running on an asus p4gd1 sporting a dothan m760 (undervolted) on an asus ct-479 and some khx3200 (the bh5 babies).
anyway, all is well and fun but for the heat that gfx puts out. even just idling around with no case and all it's sitting at about 60°C - which is too much.

so got me a recent copy of rivatuner and went about underclocking it to as low clocks as possible. and lo and behold.. temps appeared to have gone up (LOL?). anyway, i've been asking my way around and people keep telling me there is no way to undervolt these cards. somehow i don't buy that. ok so i got nibitor and fiddled around with it, saved my original bios and tried to edit it using aforementioned tool - no deal, as the tool has the voltage settings grayed out - wtf?

so here's the big one...

is there any way to mod this card to use less voltage? like some hardmod, remove a resistor and replace it with something with less resistance or does anybody have an actual bios for these type of cards that has been modded to supply different voltages (lower volts preferred - for obvious reasons)?
if so, holler!

[mpilchfamily]

Most people don't try to undervolt there cards so its not something with information readily availible. With lower end cards and lower power cards being cheap its east to move to a lower end card. Besides undervolting the card would cause it to have constant problems. Sure it would have lower temps because the card probably wouldn't work any more.

[sky]

thing is i consider a gf6600 pretty much as low as you can go. besides i need it to be a pcie card - and back then there wasn't much of choice price wise.. i don't fork out +50 bucks on a card that is utter crap for anything really. tbh i'd prefered to put a matrox millennium in there or something like it with just about enough power to give me 32bit windows in 1280x960... but there was no such thing well not for pcie anyway... nowadays you get low end ati cards and all that..
this card, in this machine, will never ever see 3d applications, so i don't give a toss if the chip is starving for voltage or not. just display windows and don't burn energy into heat that's of no use to me.. that's my gripe with it ;)

[Boogerlad]

do a vmod for the 6600gt except you start off with the vr at minimum resistance?

[Per Hansson]

do a vmod for the 6600gt except you start off with the vr at minimum resistance?

Absolutley not!
That will fry the card instantly, those vmods can only increase the voltage
Setting the resistance to zero basically tells the voltage regulator that no power is getting through so it will ramp it up as far as it possibly can and fry everything

To reduce voltage you will need to desolder the resistor that is being bypassed by a voltmod and in it's place put a pot in it's place, this will allow you to lower the vcore

This is of course allot harder to do than a basic voltage increase only vmod...
And depending on your card it might be done differently to how I describe

[Boogerlad]

oh, sorry. I'm stupid. I don't know that much about vmods.

[largon]

Yes, it's possible and it's just as easy as an increasing-type of vmod - what Per Hansson described works but there's another way in which no desoldering is needed.

What Boogerlad said is not the way, though.

[StAndrew]

Yeah, that would just make a parallel circuit. You need to replace the vGPU resistors with higher resistant ones or somehow incorperate a second resistor in the series. You can measure the resistance with a multimeter...with the card de-energized of course. I cant help you much further than that, unfortunately.

This would be a very advanced project. If you dont think you'er up to it, just get a new/cooler runnig card (you can get a GPU now for well under $100. I think the NVIDIA 9400 is a passively cooled, non SLI, almost unworthy of the name GPU, GPU) or better heatsync.

[largon]

StAndrew,
There's no need to replace any resistors, phase supply voltage can be lowered by adding one single resistor (VR eg.)... Traditional "increasing vmods" work by lowering the voltage the feedback pin senses. We only need to raise the FB voltage artificially to make the buck controller think the fets are pushing out too high volts -> buck ctrl will pull the fets lower. The easiest way to do this is by putting a VR between live vGPU voltage and FB pin.

[Per Hansson]

StAndrewThe easiest way to do this is by putting a VR between live vGPU voltage and FB pin.
But you will still need to remove the resistor going from the FB pin else you will have two voltages competing?

[largon]

Nope.
If removing resistors was necessary one would have to remove resistors even when doing incremental mods.

[StAndrew]

I think this is above my understanding. I thought that volt mods worked by lowering the resistance through a second resistor in parallel => [1/R = 1/R1 + 1/R2 + 1/R3] where R is lower than the lowest Rn in the circuit. I guess I need to read up a bit more on how GPU power input works!

Thanks for shooting me straight there largon. Hope you didnt start ripping of resistors there Sky!

[sky]

well i haven't yet started on modding the card yet, work and all that. but basically you're suggesting what i was thinking all along. i think i'll go about measuring my card one of these days. i got 2 of them anyway - one each in my servers - identical setup basically. and see what's what. will also go looking for 6600gt vmods for more juice so i see which pin\ of the ic is the fb one. and then take it from there.
somehow i was just hoping for a non-hardware mod. but then again, i'm not afraid of doing vmods. have done a few in the past on ati cards and mainboards mostly though (3.3v to ram slot, vdroop, etc)

thanks for your input guys!

[largon]

I think this is above my understanding. I thought that volt mods worked by lowering the resistance through a second resistor in parallel => [1/R = 1/R1 + 1/R2 + 1/R3] where R is lower than the lowest Rn in the circuit. I guess I need to read up a bit more on how GPU power input works!They indeed work by lowering the resistance of a certain resistor; incremental mod works through a resistor connected between FB pin and ground. Thus if you lower the R, the voltage the FB pin is exposed to goes lower -> buck ctrl demands higher voltage from the fets.

[StAndrew]

They indeed work by lowering the resistance of a certain resistor; incremental mod works through a resistor connected between FB pin and ground. Thus if you lower the R, the voltage the FB pin is exposed to goes lower -> buck ctrl demands higher voltage from the fets.

AAhhh.... Makes sense now :idea:! Thanks for clearing that up :up:.

[largon]

sky,
If you need help with the "reverse mod" feel free to drop a PM.
:)

[Per Hansson]

Yea, that sounds right
And even then he should be able to take the voltage from any source like a molex connector aswell? (making the mod easier to do)