Kramy

@Mods: First mod to see this, please move into the FAQ section.



Recently I volt-modded my eVGA 7900GS. I made a few mistakes, and learned some things when doing it, so here's what I've learned.

Warning: This post/article involves a lot of reading!


Before attempting my first volt-mod, I read these:
-7900GT vmod guide
-Which pencils are best for volt-modding.


Here's an expansion to those guides - complete with stolen images! I included everything most relevent, and a lot of stuff not mentioned. But, you should still read the 7900GT guide first, because I left out a few details that might be important.
I uploaded the images to overclock.net, in case that 7900GT guide ever goes down.



Contents
-Multimeter
-Pencils/Silver-Ink
-Removing Mistakes
-Backside of Card ---- images from 7900GT vmod guide
-GPU vmod ------------ images from 7900GT vmod guide
-Memory vmod ------- images from 7900GT vmod guide
-Maximum Memory MHZ
-Temps after vmod



First up - the multimeter:
-To measure volts, power must be flowing through the card - that means the card must be plugged into the computer, with your computer on.

-To measure ohms, power must not be flowing through your card - unless you want to fry it!

-I chose the radioshack multimeter - make sure you stick the black end somewhere grounded where it won't fall out. My case has tiny screw holes that hold it in pretty well.



[Pencils and Silver-Ink]
-Pencil lead(graphite, and some other stuff) doesn't stick well. If you want your GPU vmod to last, do it with silver ink.

-Opposite of what you'd think - it's better to use less pure pencils for shading resistors(memory vmod). I found that the graphite from a 4B pencil didn't even stick to the resistor - I had to use 2B, and only a tiny amount of shading had to be done for me to pass the amount that would fry the card. That's why measuring the ohms of the resistor before putting your card back in your system, is important.

-I had to lightly tap the resistor with the eraser to get rid of some graphite. Using an HB pencil might be best for memory vmods, but using a 2B left a layer so thin that I didn't have to rub the eraser to remove it.



[Removing Mistakes]
-Some Q-Tips dunked in 99% pure Isopropyl Alcohol can remove most mistakes.

-Try to get Q-Tips that don't shed tiny fibers.

-Try to get Q-Tips that don't shed tiny fibers, when they rub against oddly shaped things like resistors.

-Most pharmacies can get you 99% pure Isopropyl Alcohol. Just go and ask them if you can get some for cleaning computer parts - a 500ml bottle is plenty!

They'll write your name down, to make sure you aren't ordering large quantities for drug production.


I suggest you get your work area comfy. I had to remove my videocard from my computer about 20 times when checking ohms and volts, for my memory vmod. How many volts an [X] ohm resistor lets through will probably vary from system to system.

So, lets get started. Most of what is below, I ripped from the 7900GT vmod article.



Backside of card. Get your bearings and figure out where everything is, from different angles. Remember - you have to measure the voltages(mem. voltage in particular), while the system is running.

-Get comfortable holding the red multimeter prong thing to the volt measurement holes, before powering your system up.



GPU VMod

-You'll need a steady hand to do this vmod - or you can be smart and cut out a paper stencil.

I just used my hand.


-Play around on paper before you draw on your card.

-When they say shake well, they mean it! My silver-ink pen had a bunch of stinky fluid that does nothing, near the tip.


Here's all the GPU voltage configs possible:



-Most people find that 7900GS's do not increase their maximum mhz from 1.50v to 1.55v. This is probably because the 7900GS has less pipes than the 7900GT, and is already power efficient. Do not go to 1.50v or above, unless you have a VF900, or aftermarket cooling equivalent.

-I've been watching 7900GS overclocking attempts; a few people have managed 720-740mhz with 1.55V. Most have managed 730-750mhz with 1.50V, which supports using only the 1.50V vmod.



Memory voltmod.

-My resistor wasn't nearly that dark, because I used a 2B pencil.

-If you're having trouble measuring the ohms, shade around the edges. Otherwise, just stick to the top.

-553 ohms came out to exactly 2.21v, for me. I have a DFI Lanparty 590(excellent voltage regulation), and Antec Neo HE 550w(excellent +12V rail regulation). Keep that in mind - Lower quality stuff tends to over-volt.

-Get the ohms to around 553-560, and then put the card back in your system. Get the multimeter prongs in place to measure the voltage, and power her up. If the voltage exceeds 2.23V, immediately power down the system. You're too high to get good results.

-I have an eVGA 7900GS(256-P2-N625-AR) with Hynix HY5RS573225A FP-14 GDDR3 memory chips, capable of 800mhz @ 2.0v, and rated up to 2.1v. The maximum runnable speed was 1992mhz, after trying many different amounts of voltage.

-I chose to leave my volts around 2.21-2.22V - 548 ohms.

Edit (70621): New link to GDDR3. Stock voltage is different now - must be new chip revision.



-Maximum stable memory speeds:
2.24V - 840/1680mhz
2.23V - 920/1840mhz
2.22V - 986/1972mhz
2.21V - 985/1970mhz <--- You want this
2.21V - 975/1950mhz
2.20V - 960/1920mhz



If all goes well, you'll soon be the proud owner of a volt-modded 7900GS.


Don't forget to get aftermarket cooling! Heat + Volts = shortened lifespan!

I have all my back-plates removed by the PCI slots, and a fan pushing air out in that direction. I have RAM-sinks on all the GDDR chips, and a VF900 cooling things down. Failure to keep things properly cooled will impact the maximum speed you can attain, and may put your hardware at risk - don't say I didn't warn you!



Temperatures w/ 1.5v vmod + AS5 + VF900:
At Boot: 35C
Idle: 37C
3DMark06: 42-43C
Warcraft III: < 40C
Supreme Commander: < 45C
ATI Tool: 52-53C.


Location: BC, Canada


Ambient Temperature: Around 20C.

Attached Thumbnails

         

__________________
-Kramy

Athlon X2 ----- 3Dmark05 11569 ---- 3Dmark06 7138* ---- eVGA 7900GS ---- 738/1972mhz stable ---- [vmod]
Athlon XP ----- 3Dmark05 6845 ------ 3Dmark06 3519 ----- BFG 7800GS ------ 460/1450mhz stable
*1152x864


Check it out! - Videocard Power Consumption Graphs

sublime0

kool

stormlobster

woot someone used my FAQ!

__________________
Overclocking is the process of forcing a computer component to catch on fire at a higher rate than designed or designated by the manufacturer.

6600 at 4Ghz
http://valid.x86-secret.com/show_oc?id=149747
What is the best pencil to use for volt modding? http://www.overclock.net/faqs/126357...-volt-mod.html
<-----Props to MadHandlez for the avatar!

Kramy

Hmm...none of the pictures are showing up for me - Hope everyone else can see them.

Cheers!

__________________
-Kramy

Athlon X2 ----- 3Dmark05 11569 ---- 3Dmark06 7138* ---- eVGA 7900GS ---- 738/1972mhz stable ---- [vmod]
Athlon XP ----- 3Dmark05 6845 ------ 3Dmark06 3519 ----- BFG 7800GS ------ 460/1450mhz stable
*1152x864


Check it out! - Videocard Power Consumption Graphs

j_canna

i can't see pictures either...

__________________

burnstudios

I wish this would work for the new 7900GT PCB layout, like i have. Good work kramy .. if anyone finds the volt mod for the new pcb layout please post about it

Kramy

Alright - re-uploaded.

Thanks. Maybe it'll save a newbie from nearly frying his/her card?

I'll keep my eyes open for a non-standard 7900GT vmod guide.

__________________
-Kramy

Athlon X2 ----- 3Dmark05 11569 ---- 3Dmark06 7138* ---- eVGA 7900GS ---- 738/1972mhz stable ---- [vmod]
Athlon XP ----- 3Dmark05 6845 ------ 3Dmark06 3519 ----- BFG 7800GS ------ 460/1450mhz stable
*1152x864


Check it out! - Videocard Power Consumption Graphs

Renegade5399

The GS has the same layout as the GTs. It should be noted that for the mem voltage mod, you're going to want to stick a RAM sink on the 3 small chips next to where you do the mod. On 7900GTs, those will be what fails first.

Bal3Wolf

i did the mod set to 2.1 somthing but clocks above 880 werent stable still i could run ati tool 3d window now but only for few secs befor screen went crazy and had to reboot.

__________________

Kramy

If I remember right, I only hit ~860mhz on 2.1v; the GDDR3 really loves 2.1 to 2.2v.

__________________
-Kramy

Athlon X2 ----- 3Dmark05 11569 ---- 3Dmark06 7138* ---- eVGA 7900GS ---- 738/1972mhz stable ---- [vmod]
Athlon XP ----- 3Dmark05 6845 ------ 3Dmark06 3519 ----- BFG 7800GS ------ 460/1450mhz stable
*1152x864


Check it out! - Videocard Power Consumption Graphs