Ok we have two Vregs for the VGPU in paralell. They are the simplest type of Vreg... put a voltage in and get one out with one pin for setting it up via a resistor devider.
From looking at the card both Vregs are on the same resistor devider thats in the pic.
I havent done this mod myself yet as I havent even tested the card :P but its pretty simple.
This first pic shows the main components...
If you put a VR over the lower resistor in the devider you should get more voltage.
I think I will just replace this resistor with a VR.
The second pic shows the different voltage planes.. should anybody want to add some capacitance.. which may be a benefit.
Originally posted by Holst On my card the lower resistor measures only 60ohms.... but i think the resistor is 98ohms.
so 10k may have no effect, but its very unlikely to cause an overvolt...
Can you check the resistances on your own card to confirm my readings 60k seems a bit low to me..?
Im looking into the Vmem mod atm.. it looks simple and complex all at the same time.
So it should be around 98ohms right? I'll unsolder one side of it to check. And if we are talking about this type of resistance, what value variable resistor should I start with? I also have a 1k 20-turn pot that I think would work better in this case... that wouldn't be too low, you think?
The memory runs straight from the 3.3v line as expected.
The VGPU is also running from the 3.3v line droped down to 2v via the mosfets... the mod will be the same however the max voltage will be lower... some people may want more than 2.5v (my estimate of the max voltage avalable)
The mosfet marked 882 on the top right of the card produces VDDQ and im currently trying to work out how it works... I cant find a PDF for it ATM but ill keep looking.
1k might be ok.. still might get a bit scary towards the end of travel... I have a better VR selection here soI think ill just swap the resistor with a 200ohm VR that way ill have much more controll.
Nice one m8, im glad it works... post results in the competition thread as soon as you can.
If you replace R223 in a similar maner you should be able to ajust VDDQ (should be 2.5v stock)
VDDQ can be measured as in the pic below.
You "may" get a higher memory clock by just increasing VDDQ.. however you might also need a big boost in the 3.3v line to get any real gains. Carefull you dont kill your card memory vmods are somewhat dangerous.
Im also still unsure as to how Vref works.. ill take a further look now.
Another option may be to cut the 3.3v line to the memory and force in another voltage... however this is a much more complex mod that would need testing... this is my eventual plan (take 3.3 to say 4v) but it will take some practical tests.
Just increased the GPU to 2.1v and then measured R224 in-circuit... it measures 66.1ohms. I guess extremely small changes in resistance affect GPU voltage modestly.
It "seems" to be produced through a the VDDQ line via a simple resistor... so it should "sort of" track with VDDQ... to get it 100% right may mean allot of tricky soldering and messing around...
However ill have to read samsungs PDF's allot further before I can say for sure how it works as ive never done this sort of thing before.. memory and associated voltages are somewhat new teratory.
I also have a "possible" solution for VDD on the memory.. however im keeping it under my hat atm..
This is great work you guys are putting together. I have only time to bench the card yesterday for a few hours and only checked voltages. Your due diligence is so greatly appreciated.
BTW....my initial results were quite remarkable, especially where the ram is concerned. Overclocking it by itself..and I have the TC50 Samsung, I attained 310Mhz throughout all 3Dmark tests with NO artifacts. 320Mhz made it through all but nature where it froze.
The GPU is like all others, and despite an MCW50T attached fed with -25c coolant 265Mhz max was attainable with only marginal artifacting.
In combination, I could run 265/300. I'll be aquiring some lower resisance VR's and attemping the volt mods myself soon.
Heres a pic of the finished Vgpu mod. I carefully removed the lower resistor in the divider and soldered in a fan pigtail. so far so good, as Jeff getting approximately 2v @ 68 Ohms. It's 2:30am as I write this, so further testing will occur after some sleep
This is a major pic size, but thought it would assist the members who have not attempted this type of mod, with a little higher detail.
I ended up using a 500ohm variable... I'd recommend the 200ohm one like Holst suggests.
To make soldering easier for people, in Randi's second picture, you can solder the top solder point to the Vregs bottom leg.
And you can solder the bottom solder point to any ground.
It's a bit of a pain to get it how Randi has it and unless your pretty good with the soldering iron you may give yourself a headache trying to copy him.
Reply With Quote
for looking into this. 
Bookmarks