Volt mods

[nickolp1974]

I want to have a bash at some volt mods but cant find a good guide, when it says fix 100k VR to ground, where on the card is ground??

Can i take it to gnd on 6pin power points?

[Pulse88]

Simple answer is yes. can be other points of card to that have ground 2. (6pin ground easiest to solder)
What card do you want to mod Nick ?

8800 gtx is a god start modding card. ati cards medium ,gtx 285 hard (diff kind of mod resistor removing involved)
gtx 275 i have is a nightmare a rev 2 board. only way to v-mod Vid table = resistor removing /soldering
decided to keep it un modded no guide....

[nickolp1974]

Just tried on a 3870, should of bought a magnifying glass whilst out!!! Think i have knackered it as the solder point has gone and i cant get a reading now, oh well it was a crap card and only a fiver.
Onto 8800gtx now, bit easier! Meant to be 400k, but can i use a 500k vr?

[Pulse88]

400k,500k No
400 Ohm and 500 Ohm Yes

Very important to not have power full solder pen 15-25w is good(with pointy tip).
To powerfull solder pen is very hard to get god solder joints on pcb.

[nickolp1974]

Well it didn't work, left a bench looping and had mm attached and adjusted VR voltage stayed the same although when i turned it fully clockwise the signal went and had to shut down power and drain, booted back up fine.
There are 3 pins 2 on the outer and one central, i had 1 cable to mod point and outer leg and other cable on inner leg to ground, either this is wrong or mod point solder did not take??

[TheMadDutchDude]

Never, ever turn it fully. You could pop the card instantly if OVP or OCP doesn't catch it in time. :/

I solder to the outer two legs as that gives the biggest amount of tweaking room.

Are you familiar how VRs work? Do you know how to work out what size VR you need?

I honestly find soldering the most difficult bit. Once you've got yourself a steady hand and are confident to just go for it, you'll be golden.

[nickolp1974]

Thanks for the info, i resoldered to the 2 outer legs yesterday but not had time to test. No idea how VR's work.
At a guess, creating more resistance allows less voltage through, so for safety i checked resistance on 2 outer legs and set for whats needed, so in the case of 8800gtx i set it to 400ohms and whilst running i turn it down which should increase the voltage??

[TheMadDutchDude]

I'm an idiot. They need to be in the middle and one of the outer edges. My apologies.

You're correct, higher resistance will lower the voltage and lower resistance will increase it.

There's one way to avoid a short circuit and that is to install a 1 ohm fixed resistor into the circuit. Kenny (K404) taught me that.

[nickolp1974]

If thats the case then maybe my mod solder point didn't take as i have tried all combinations. Going to grab myself a magnifying glass before i attempt any more, must be my age!

[nickolp1974]

Got a couple of 295's coming and there appears to be an easy mod for these, anyone know the max volts i should be pushing for under water?? I'll then know which resistors to remove.

[Pulse88]

Just tried on a 3870, should of bought a magnifying glass whilst out!!! Think i have knackered it as the solder point has gone and i cant get a reading now, oh well it was a crap card and only a fiver.
Onto 8800gtx now, bit easier! Meant to be 400k, but can i use a 500k vr?

Alternative solder points(marked blue) for 3870 ref From Swedish overclocker Calathea.
So Nick your card is not out of hope yet to v-mod.
100k vr between FB leg or alternative solder points to ground.

[nickolp1974]

Cheers Pulse for that, i have not tested the card yet but i fear its had it due to a trace being pulled out.
Bonus on the 295's, no volt mod required as i can get iirc 1.4v with afterburner although i'm limited to about 1.2v due to temps, need to find some blocks, so if you see any for dual pcb give me a shout

[Luumi]

Does anyone know is there an easier way to route very bad OVP and OCP on PX3544BDSG controller? Both seem to trigger at around 1.38v.

Picture here: http://img.popspace.com/upimg3/grab/mob ... 818331.jpg

[ObscureParadox]

This is how you go it on a 8800GTS with the same controller, should be transferable with some adjustments to the VR. ]

Edit : Misread original IC number, part is slightly different

[Pulse88]

@Luumi
Hmm think some 8800gtx/9800gtx/8800gt/gts and 9600gt have that controller (PX3544BDSG)
What card is it, like pcb version etc?

[Luumi]

It is EVGA 9800 gtx + SC, I can't find pcb rev but it does have PX3544BDSG controller. I've tried pretty much everything now and I can't get over it...

I've tried all like on this:

Now I even short those OCP pointed resistors as 1 of them dropped off. Card works but at 1.38v the whole system shuts down and resets instead of 0v on all voltages. Can anyone help me with this?

[Luumi]

Actually the whole thingy seems to be OCP. I even removed the ovp resistor and its not it.

But im sure the OCP points in that pic arent correct. TIN at kingpin forums told me to increase resistance on the isen points but which resistors are they?

[Pulse88]

Ok have you checked with multimeter that your pcb have the same ocp resistors same ohm(revisions of pcb,controller number can change place or amount of them). If that is done take one X k VR.



But pararell soldering resistors with Vr from your picture. Now vr change ocp

Bad paiting skills sorry

[Luumi]

The controller is PX3544BDSG, with bottom row being 5107 KR.

Funny that I can't find pcb rev anywhere. There is MEC4 text just above the pci-e teeth.

[Pulse88]

compare layout around controller vs your picture with ocp and card you mod. Your picture of 5107 seems to have same layout as 5007 (g92 ref board)controller. Ohm of resistors is likely different from your card to ref 9800gtx +.

Since they are none data sheet on that controller for public.

Take a multimeter and ohm the resistors the ocp resistors should have same value. (to find all ocp resistors)

You can also find ocp pin of controller by taking redcable + on controller pin and black cable - on the plus side of one ocp resistor. You want 0ohm on multimeter then you have find the pin.Then after you find pin you can search for resitors around controllers if they are any more ocp resistors for your card ( the same method as searching for alternative solder pints for v gpu mods)

My guess your pick with ocp resistors might be right if they all give same ohm value and layout are the same around controller as your pick.

But it is hard to help when i not have 9800gtx+ sc card...

[Luumi]

Okay here: http://i.imgur.com/FleAIh4.jpg

The blue ones are all around 75 ohms. I tried all these shorted and it didnt affect anything. I think they are PWM resistors as found in the datasheet. The red resistors are all 5k ohms except the lowest one is 25Mohms as you can see there is no resistor placed next to lowest green brown cap. The brown caps are for sure part of the Isense circuit.

I think the red and green dots make the Isense circuit together as there are 4 phases on the card. But should it work if I just double or triple the reisstance on the top ones as the bottom one is already so huge.

[Pulse88]

Never tried a vr with blue resistors Luumi?.

Maybe the controller dont like shorted resistors for ocp

with 4 phases Blue resistors seems more right, when they all have same resistance.(75 ohm)
My answer would be to try 1-2k Vr without short the blue resistors before you test red ones for ocp.

But to be honest weirder things have been right before in v-moding.


I hope you solve it Lummi

[Luumi]

I did try VRs on the blue ones, then resistance dropped to like 65 ohms but still the same. Then the top blue one came off also afterwards ;p. Its not the blue ones I'm pretty sure.

[Pulse88]

Tried 100k vr on red ones Lummi for any luck disabling ocp?

[Luumi]

Tin told me to put same ohm smd resistors over them. Doesn't that mean to increase resistance? He said it would double ocp limit.