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post #1 of (permalink) Old 09-07-2017, 02:09 PM - Thread Starter
mllrkllr88
External VRM FTW
 
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Join Date: Apr 2008
Location: Portland, OR
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General GPU Voltmod and External VRM Information

Welcome!

As many of you know I have been spending lots of time modding GPU's for OCN team members and myself. After doing over 100 voltmods I have learned a few things and I want to share what I have learned here with you guys. Not much of this information is new, you can find quality information scattered everywhere around the web. My goal with this thread is to collate everything I have learned into one cohesive source.

The goal of this thread is to provide general information universal to all GPU's. I will not be providing much information pertaining to specific GPU's.

This document will be a work in progress.
Basic GPU Volt Mods

Section 1: Introduction
If you are reading this then you likely don't need much of an introduction into overclocking, so I will skip the newb stuff.

There are two main ways that the PWM controller can increase the voltage to the core. There is the feedback loop method (FB) and the sense method (+Vsen). In both cases the maximum PWM output voltage is set by an external resistor network. Lowering the resistance of the FB or +Sense pins, will in turn raise the maximum voltage of the of the PWM.

In modern cards there will be different voltage and power states which can throttle down both the number of active phases and voltage. However, lowering the resistance of the external FB of +Sense resistor network sets the maximum output voltage during full load conditions.

Section 2: Examining the GPU
Step 1: Locate the PWM controller
The first step is to identify the voltage controllers of the card. This can be really confusing at first but once you do enough of them, they will become easy to spot. In most cases the core and memory PWM controllers will be QFN package parts, but on older cards or low power cards they can be SOIC packaged parts (google those if you don't know the package names).

The trick is that in most cases the PWM controller will be very close to the choke/driver it controls. Therefore, the first step is to identify the large inductors and you can be fairly certain that the PWM will be close by. Here we have a basic reference GTX480 as an example



Step 2: Find the corresponding PWM datasheet
After you have identified the target PWM controller, the next step is to find the datasheet that tell you the pin assignments. This is often the most difficult part to modding GPU's because many of the datasheets were never released or are still NDA. The now famous engineer TiN over at EVGA currently has compiled a database on his website xdevs, this is the best resource for finding unreleased or NDA datasheets. The datasheets he has made available to us are searchable via google.

Step 3: Measure the resistance
Once you have the datasheet then you should be able to easily locate the important pin that was mentioned earlier. You are looking for a pin marked "FB" or "+Sense" (sometimes called VSEN or VGPU). Here are a few examples of what you are looking for, they also happen to be hard to find datasheets



There will be a marking on the IC and a marking on the datasheet IC so you can orient yourself. Once you have correctly located which pin you will be working with, take your measurement from the very first discrete part you see connected to the pin. You should never have to work with the pin itself, always work on the parts connected to the pin. In rare cases the pin you need will be underneath the PWM, but that is a problem for a different section of this guide.

Working with the GTX480 example again, you can see it uses CHL8266 and the pin you want is VGPU (pin 4). In this particular case, I measured a resistance of 1.6 ohms. Write down this number because it is the most critical aspect to the voltmod.




Section 3: Parts and Preparation
Step 1: Choose a potentiometer value
In step 3 of section 2, you figured out the stock feedback/sense resistance of the PWM you wish to control. There is a very simple formula you can use to determine the appropriate pot value. Simply multiply the FB resistance by 23 and then choose the next highest standard potentiometer value.

Using the same GTX480 as an example, we measured 1.6 ohms for the core FB/Sense. In this case we take the stock resistance of 1.6 ohms x 23 = 38.8. Given that number, I know the next highest pot value will be 100Ω, so that is the part I will choose for the mod.




Below, you will find a list of all the "typical" potentiometer values followed by the code that is printed on the pot itself.
  • 100Ω (101)
  • 200Ω (201)
  • 500Ω (501)
  • 1KΩ (102)
  • 2KΩ (202)
  • 5KΩ (502)
  • 10KΩ (103)
  • 20KΩ (203)
  • 50KΩ (503)
  • 100KΩ (104)
  • 200KΩ (204)
  • 500KΩ (504)
Choosing the correct pot value is critical because this will determine the controllability of your mod. If you choose a pot that is too small (under 20x multiplication) then the new idle voltage will be much higher than normal. Conversely, if you choose a pot value that is too large (greater than 30x multiplication) then the mod will be difficult to control at higher voltage. In most cases, the simple formula of 20-25x will be correct.

Step 2: Prepare the potentiometer
Firstly, unscrew (counterclockwise) the potentiometer completely, this might take 10+ turns and in most cases you will here a little click when its fully unscrewed.

You will need to trim the pot legs to decrease the possibility of shorts and mistakes. Below is an example of a perfectly prepared pot. You need to remove one leg completely and I suggest trimming the legs a bit.


I like to add little disable switches to my pots. This allows me to easily enable or disable the mod completely. Using this method, you can run a card 100% stock and then easily enable the mods when you are ready to bench. There are several advantages to this method. If you wish to take this unnecessary step, simply trim the pot and the switch, bend the center leg of the switch, add a tiny dab of super glue, then solder the switch in place.



I like to add nice long wires to my pots and use shrink tubing. Sometimes I will prepare a bunch of common sized pots so I have them ready when I sit down to do a bunch of mods. I use 28 gauge wire and 1/8" shrink tubing.



Section 4: Putting It All together
Now that you have your potentiometers all prepped, and you know the where the mod points are, its time to solder it all up. I like to use hot glue to affix the pots to the card itself. Once the glue dries then I test route the wire and cut them to the length I think I will need.

In almost all scenarios, you should solder one lead of the potentiometer to ground. You can get ground from hundreds of locations on the card, but I like to use the 12v PCIe connector.

If you prepare everything by tinning it with solder first, it will make the connection much stronger and it will make things easier for you in the end. Add solder to the solder point you have chosen on the GPU. Then I strip the wire (remove about 1/8) and tin the wire. The secret is to clip the exposed wire super short after you have tinned it. If you did the prep work correctly, you should be able to quickly and easily solder the wire to the mod location.

If you want to add a nice finishing touch to your mod, then spend a few extra $$ and get voltage displays. I will cover them in the parts section later. The displays require a voltage source, I get +12v directly from the PCIe connector.




Voltage display wiring:
  • Red = +12v from PCIe
  • Black = Ground from PCIe
  • White = Voltage read point (choke or choke cap)
Where you place the pots and displays is up to your own personal style. I have tried lots of different configurations myself and I definitely like the pots to be accessible from the back. Here is an example layout of pots and voltage displays.



Section 5: Testing
I have often been asked how to test the voltmods and unfortunately there is no generic answer or mathematical solution. Voltage scaling, voltage tolerance, and voltage limits are all factors that are unique to each card. I tried to come up with a generic % increase formula in the past but it really just doesn't work out, so instead I will give you some guidelines to work from.

Core Over-Volt
In most cards you will reach a point where scaling stops either because of the silicon or the temperature. There is no secret sauce to figuring out the correct voltage, it just takes time and patience.

The best advice I can give is to start small and increase slowly to see what effect increased voltage has on the card. I typically don't push much more than +250mV for old cards and +150mV for newer cards (assuming very good cooling with temps under 60c). Again, each card is different and those numbers might not make sense so keep that in mind.

Memory Over-Volt
Most cards just don't scale much with memory voltage. When I get a new card I start with +10mV and see if there is any scaling from that. If I see a scaling improvement, even a tiny margin, then I keep increasing and testing up to about +100mV. Heat could be a factor so keep that in mind.

Memory voltage increase can help in other ways. When you are running LN2 with Samsung and other's, adding lots of memory voltage can stop the memory from having cold bug issues. I have not tried this myself but I have herd that sometimes it can take +500mV to generate enough heat so as to combat cold bugs.



Advanced GPU Mods


Section 6: OCP/OVP Limits

Section 7: Capacitors
Nice read: LINK

Section 8: Switching Frequency

External VRM GPU Volt Mods
Zombie Power Card Voltage Regulator
-LM2596 DC-DC Buck Voltage Regulator
-Ebay Search String: "LM2596 DC-DC buck adjustable step-down"
-Ebay Link: LINK

Power Card: GTX580 Lightning








Power Card: 8800GTX



Tools, Parts, and Supplies

Modding Supplies
Potentiometer
-Style 3296, multi-turn
-Ebay Search String: "60PCS 12value 3296 W Potentiometer"
-Ebay Link: LINK

Disable Switch
-Style: SPDT 1P2T
-Ebay Search String: "SS12D00G4 SPDT 1P2T 2 Position 3 Pin"
-Ebay Link: LINK

Wire
-Style: 28 AWG Gauge Stranded
-Ebay Search String: "28 AWG Gauge Stranded Hook Up Wire"
-Ebay Link: LINK

Heat Shrink Tubing
-Style: 3/64" 2:1 ratio
-Ebay Search String: "3/64" Heat Shrink Tubing 2:1 Ratio"
-Ebay Link: LINK

Voltage Display
-Style: Mini DC 0.1-30V LED
-Note: There are many bad voltage displays out there. If you buy something other than the one I like, please make sure it has the small adjustment potentiometer on the back. Also make sure it lists the measurement accuracy at 0.1%
-Ebay Search String: "Mini DC 0.1-30V LED Panel Voltage Meter 3-Digital Display Voltmeter Motorcycle"
-Ebay Link: LINK
-Check out this thread for testing: https://www.overclock.net/forum/189-...l#post28397452

Solder
-Style: Kester 44 Rosin Core
-Ebay Search String: "Kester 44 Rosin Core Solder 60/40 24-6040-0027 "
-Ebay Link: LINK

EPower Copper Plate
-Style: 1mm thickness
-Ebay Search String: "Pure Copper Cu Sheet Thin Metal Sheet Foil 100x100x1mm "
-Ebay Link: LINK

Prototyping PCB's
-Style: Double-Side
-Ebay Search String: "Double-Side Prototype PCB Board"
-Ebay Link: LINK

Generic Mosfet Heatsinks
-Style: 11 x 11 x 5mm
-Ebay Search String: "11 x 11 x 5mm Adhesive Aluminum Heat Sink For Memory Chip IC LM02"
-Ebay Link: LINK

EPower Long Handle Pot
-Style: For EPower V4 (RED), 1K, 3296 w/ RA handle
-Ebay Search String: "1K Ohm Multi-turn Trimmer potentiometer 3296 w/ RA handle"
-Ebay Link: LINK

Voltage Regulator for Power Cards
-Style: LM2596 DC-DC
-Ebay Search String: "LM2596 DC-DC Adjustable Buck Converter Step Down Module Power Supply 1.23V-30V "
-Ebay Link: LINK

Kapton Tape
-Style: 10mm wide
-Ebay Search String: "10mm 1.0cm X 33m 100ft Kapton Tape High Temperature Heat Resistant Polyimide "
-Ebay Link: LINK

FLux
-Style: Kester 985M
-Ebay Search String: " Kester 985M NO CLEAN FLUX PEN "
-Ebay Link: LINK

Capacitors
Cheap but effective core/mem electrolytic
-Style: 820uF 6.3V Panasonic FJ
-Ebay Search String: "820uF 6.3V 8x11.5 Panasonic FJ Low ESR 6.3V820uF Motherboard Capacitor "
-Ebay Link: LINK

Medium quality core/mem electrolytic
-Style: 820uF 2.5V Aluminum Solid
-Ebay Search String: "820uF 2.5V Utrla Low ESR Aluminum Solid Capacitor"
-Ebay Link: LINK

High quality core/mem electrolytic
-Style: Sanyo SEPC 2.5V 820UF OS-CON Aluminum solid
-Ebay Search String: " Sanyo SEPC 2.5V 820UF OS-CON Aluminum solid Low ESR Capacitor"
-Ebay Link: LINK

Special polymer electrolytic SMD
-Style: 100uF 6.3v
-Ebay Search String: " "
-Ebay Link: Need to update this


Tools


EPower Soldering Iron
-Style: 150w 120v
-Ebay Search String: "150w 120v Soldering Iron Soldering Solder w Chisel Tip "
-Ebay Link: LINK

All-Purpose Soldering Iron
-Style: 852D+
-Ebay Search String: "2 in 1 Soldering Rework Stations SMD Hot Air & Iron Gun 852D+ "
-Ebay Link: LINK

EPower Copper Plate Snips
-Style: Straight Cut
-Ebay Search String: "12" Tin Snips Sheet Metal Straight Cut Heavy Duty "
-Ebay Link: LINK

24/7 BENCH
(9 items)
CPU
[LGA115x] 8700k, 7700K, 7350k, G3258
CPU
[LGA2066] 7940X, 7740X
Motherboard
[OCF FTW] X299 OCF, Z170M OCF, Z97 OCF
GPU
E-Power, G-Power, H-Power, A-Power
RAM
B-DIE, HYKO, PSC, MFR
Power Supply
Seasonic Prime Platinum 1200W
Cooling
Kingpin Cooling: Venom & T-REX
Cooling
2x360 RAD Custom Loop
Case
Dimastech Easy V3.0
▲ hide details ▲



Last edited by mllrkllr88; 04-06-2020 at 07:16 AM.
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