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GTX 670 reference PCB - voltmod

post #1 of 94
Thread Starter 
Hey everybody,

this is my first post here. I think I have finally found a forum, where fellow enthusiasts like to share thoughts and information. I'm new to voltmodding GPUs, but I am quite experienced in electronics. There is a lot which I don't know, but only little I can't learn. I may be wrong in my arguments and wish to be corrected! This is how I learn =)

I have a rather good Palit GTX 670 Jetstream. It runs 1350MHz core 24/7 with just the modified bios. I do have watercooling (check out my rig!thumb.gif). The card still runs very low temps, so.. hunger grows as I eat =)

I have not found any completed voltage mods for GTX 670. Now I do mean reference PCB models.. This feels odd considering the popularity of this card! I've read about TIN's GTX 680 mods. Also I've checked out many other mods. I find it displeasing how in many cases the thought is not delivered 100%. Only the wiring...

Well, about TIN's method. In his article he hardwires VID pins. This way bios cannot control the voltage at all. Although my GTX 670 uses a different PWM circuit (NCP5392), I found the VID pins follow the same standards. Same amount of pins and same combos give same results in Vout. I'm sure the two most significant VID pins are hardwired just like in 680. Also the unlocked bios voltage range speaks in favor of my argument. If MSB is tied to 0 and second MSB is tied to 1, the voltage range is 0.81875 V - 1.2125 V. Therefore I'm quite sure this method is available for GTX 670! This is not a very nice way, because you have zero control via bios. The card will have a solid voltage. The bios cannot change the voltage by load. Also this method requires cutting of many traces and a lot of soldering. The card could never be restored. Warranty is lost when I put the waterblock on, but still I prefer to do stuff so that I may undo it later =)

Another way could be to alter the feedback. This way you could slide the voltage region higher. Bios would think it's changing the voltage inside 0.82-1.21V, while the voltage region truly was a tad higher instead. This is the mod I'd feel comfortable with. Now then.. Which contact to alter?

The PWM chip of GTX 470 is a close relative to 670's. I've looked at some 470 mods. This one seems to connect VR (100ohm) between VS+ and VS-. I totally get this! Core voltage is connected to VS+ pin, while core GND is at VS-. You pull down the feedback input (VS+) to lower the feedback voltage. This requires there to be notable resistance between VS+ and the actual core voltage. If the contact is low impedance, the VR won't do much.

Another signal I thought about pulling down is the VFB signal. I'm not sure about this because there are other circuits it might mess up..

I put some serious thought into this, hope you guys read biggrin.gif
I appreciate all feedback and help!
post #2 of 94

the mod for GPUv with the NCP5392 controller is with VR to pin 17

 

 measure stock resistance and multiply value by 20x for approximate VR size required for mod

 

short pin 12 to ground to remove all OCP function

adjust resistance at pin 10 for power switching frequency

 

**You should not have to bother with VID if you do both GPUv and OCP mod..   moving VID = moving OCP... moving GPUv alone does not.. this is why OCP mod is required if you mod for GPUv with VR and not VID.

post #3 of 94
Thread Starter 
Hey! Thanks for the quick and informative reply!

So GPU voltage is increased by pulling down the VFB pin as I first thought. The resistance you mentioned must be the RFB mentioned in application schematics. Just to make sure, you do mean pulling the pin 17 to GND with a VR, right? This makes sense.

About OCP protection then. Does the card measure the power target by this?
It seems to me like pin 12 (IMON) measures the current value by voltage over a shunt resistor. Application schematics don't tell, but this is the usual way. But if this is the way, then I don't understand how VID's affect overcurrent protection. Please explain!
Description in datasheet: IMON: 0 mV to 900 mV analog signal proportional to the output load current. VSN referenced
If I'm right and find the shunt resistor, I could lower the resistance with a fixed value resistor. This way I could actually get useful information about the power draw.

I'm not sure if OCP is necessary for me, if I only slightly increase the Vgpu. Currently I'm thinking about 1.25-1.3V. My card seems to have very low current in stock. Even as I have overclocked my card (pics), the power% rarely goes over 100%, never over 105%.
post #4 of 94
Quote:
Originally Posted by Olper View Post

Just to make sure, you do mean pulling the pin 17 to GND with a VR, right? This makes sense.
Thats correct. thumb.gif
Quote:
About OCP protection then. Does the card measure the power target by this?
No, its for Over Current Protection
post #5 of 94
Thread Starter 
Ah ok. OCP is for the PWM circuit only.. The power% measuring must be from the 12V line.. I wasn't thinking clearly. I work with power supplies that convert from 400VAC to 24VDC. With these power can be accurately measured from various places. It's very hard to measure curret from a 1V line.

Did i see correctly with this 470 mod: http://img202.imageshack.us/img202/4119/82539415.jpg
Is the VS+ and VS- connected with VR?

Also, do you know any other GPUs that have NCP5392. I'm interested to see completed mods =)
post #6 of 94
Quote:
Originally Posted by Olper View Post

Ah ok. OCP is for the PWM circuit only.. The power% measuring must be from the 12V line.. I wasn't thinking clearly. I work with power supplies that convert from 400VAC to 24VDC. With these power can be accurately measured from various places. It's very hard to measure curret from a 1V line.

Did i see correctly with this 470 mod: http://img202.imageshack.us/img202/4119/82539415.jpg
Is the VS+ and VS- connected with VR?

 

ok. one thing at a time smile.gif

 

 IMON = OCP.. it samples current draw through the mosfet stages... lowering resistance will effectively lower the reported current, in-turn, increasing OCP limit

VID = programmed output [by default a set VID will have a tolerance for OCP.. like +/-20% of VID value for example] ... this is why modding GPUv with VID also increases your OCP limit

 

 If you do not mod for VID.. then you very likely MUST mod for OCP. You may be alright adding +.15v to core... but if you encounter black screen on load, with GPUv reset to '0.01'v .. then you know you hit OCP and need to adjust.

 

**As for the pic.. no that is not -VS and +VS .. its just pin17 FB [dot closest to IC.. connection on the lower right...] and the other connection is ground off of the FB resistor.

 

 

 Its important to keep in mind that when you mod for FB - your mod point must measure to FB, and also have continuity to ground. wink.gif

post #7 of 94
Thread Starter 
Thanks for the clarification on VID affecting OCP. I might lower OCP resistance by say 30%. Or just short it =) I guess there is no need for OCP if the device is working properly..

The 470 mod still bugs me. For this IC, the FB pin is not 17, but 19 according to datasheet (link).
This image (link) shows the tracks well. When compared to the mod (link), it really looks to me like pins 15 and 16 are connected by VR. Testpad for pin 19 (FB) is to the right.
post #8 of 94

well i dont know what to tell you other than your mistaken. mod for NCP5392 is definitely with pin17

 

 Grab a DMM.. 

 

 measure pin17 which is FB 

 measure indicated connection points on pic for mod

 

 

 You will find its as I described. Your looking at 2x different IC controllers.. the mods are not the same.. dont get them confused.


Edited by CL3P20 - 11/24/12 at 9:22am
post #9 of 94
Thread Starter 
Yes, for NCP5392 it is pin17. For GTX 470's NCP5388 the pin is 19.. In the GTX 470 mod, i think VS+ and VS- are connected by VR. If there is any resistance between VS+ and Vout, i totally get this mod. What i'm wondering is if similar would work for NCP5392 =)

I'm not saying VFB mod wouldn't work. I'm only interested in all options. I need to know how stuff works biggrin.gif
post #10 of 94
Thread Starter 
Is the switching frequency mod very common? Is there a good reason to mod it... I know with higher frequency you get less ripple which is nice, but you also get increased switching losses.. I'd prefer lowerin ripple by adding capacitors, if it ever was an issue. My goal is not extreme LN2 overclocks, so I don't think I HAVE to do any of this.. But if I see unpopulated pads for capacitors, I will fill em up =)
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