The 7900GT is basically an under-volted, and hence underclocked, version of the 7900GTX, with a cost delta of about Rs.12,000. The GTX's core/processor is run at the rated voltage of 1.4v, while the GT is run at 1.2v. Even the Samsung memory chips are underclocked here at 1.8V from the default 2.12V in the GTX. Now, if only I can increase the core and memory voltage by 0.2V (or more), I can "stick it to the man" and overclock my relatively cheap GT to GTX speeds (and beyond) for cheap! And thus began my journey into hard mods, which here it's specifically called a "volt-mod". This is not a tutorial for volt-modding your 7900gt, however, since there are quite a lot of that out there.
Anyways, soon after the hard launch of the 7900GTs, many different mods for increasing the core and memory voltages came out. Almost all of them came out on xtremesystems.org. The mods ranged from easy(connect dots with conductive ink pen) to n00b-killer higher-volt volt mods (replace resitors with variable resistors and solder-in connections). I chose the easy mod partly because of not wanting to push my beginner's luck too much, and partly because I don't have a good third party cooler. That conductive ink pen was nowhere to be found around my area. I could've went over to the electronics center of my city, the Ritchie street, coz I heard it through the grapevine that it could be available there, but I was too lazy to plan a trip there.
So I settled to buying soldering equipment locally. Now, I've owned a soldering iron before, about 5 years ago I think, but I don't remember using it more than once, unsuccessfully, before it went kaput and I had to throw it away. With such soldering talent, I thought it would be wise to wisen-up before I burnt my house down. So I took the family's TV remote (at night when everyone was sleeping, of course) and tried soldering test pieces of wires onto the components and then de-soldering them. This was also the first time I had held and learnt to use a DMM, Digital Multi-Meter. After reading a few articles on soldering and DMMs, I can say that I can do some basic solder mods with some confidence.
Tools of the trade: The buying power of Rs.280
Here's the 1.55 volt mod I did. I have a closer-up version but it looks like a -20 myopic's view of the night sky: (yea, I know, try to buy a real camera)
Make no mistake, these "solder pads" are tiny and soldering these things can be very tricky without a soldering rod that is thinner, sharper and more suited to electronics solder. I couldn't buy one so, before modding the video card, I tried modding the soldering rod itself. First, I tried to the brute force method of making the rod thinner, i.e., filing. Having no proper file, it was getting tedious to remove any amount of copper off the rod. So next I just took a stiff bit of bare copper wire and wrapped it around the rod a couple of times, leaving a small piece of copper jutting out. The way I used this copper wire is like this: first I melted some solder on the main copper nose and sort of splattered the tin onto a heavily taped area on my table. Then I looked for a tiny enough globule of tin that can be remelted by the copper strand, and then used the copper wire as soldering rod tip. The reson for splattering hot solder and then using that instead of using the solder directly from the spool is, the copper wire won't have enough heat to melt such a large diameter of solder wire.
This method was quickly becoming slow, painful and messy (to say the least), so I wound up doing all the solders without the copper wire mod. Anyway, here's the glorious copper wire mod simple mod, which can, almost, be seen below :
Personally, I would recommend you to wait and get some silver paint or a conductive pen to perform this mod. If you do choose to solder mod your card instead, get to know the proper usage of the soldering gun and the DMM before you even switch them on. I had many close calls and nearly blew my card. Also, try to buy as many implements as you can that would help you solder better. For example, magnifying glass, tweezers, desoldering braid, gloves, etc. Here's some tutorials to prep you up: SMD soldering[sparkfun.com] & Modding & DMM[madshrimps.be].
Finally, onto the mod itself. Let me put what I know about the mod simply. The new gpu has a set of Voltage ID (VID) lines which carries the code for the voltage to be supplied from a sortof voltage table. The vmod changes the VID by connecting some of the VID lines to one of the ground points (to produce logical '0'). This makes the VID point to another voltage in the voltage table. From what I understand, in older video cards, modding relied on changing the electrical properties of the traces/SMDs themselves to transmit a higher voltage. The current type of mod is a major improvement over those kind of mods. Anyways, below are the two major places on the PCB to mod:
The first 'opcion' (spanish, I guess) in the first picture is the easiest to do, followed by 'opcion 2' and then the third mod (the second picture). First, I did the first mod but now I am with the second mod. I'll say the reason for jumping mods a little farther down. The scales involved in the third mod are just a tad tiny for me to solder properly. Not that I didn't try though. But it's too small for even my 'ghetto copper wire mod'. Next time, I am going to buy a magnifying glass and try to clean up the mod.
To over-volt the memory, there's a so-called "pencil mod". A pencil mod is done by shading the top of a resistor element using an ordinary lead pencil. Lead in the pencil is a pretty good conductor and acts as an alternative path, effectively reducing the resistance of the element. The DMM comes in pretty handy here to know if you've shaded enough or if you need to erase a few lines to get to the target resistance.
I didn't even bench the card at stock. I directly went and did the 1.4v mod and the 'pencil mod' for the memory chips, and hit 630 core and 784mem (Stock 450 core, 660 mem). Since I don't have a third party cooling solution for my video card, I didn't know how much excess heat the stock coolers can dissipate once over-volted. The temps were in the vicinity of some high 80s. Then I did the 1.5v mod after making sure the video card's not melted and was able to go upto 680/900.
The peak temperature now was peeking at 100°C! Most people I know would've suffered some sort of massive attack if it were their card. But I kept this setup for a few days and then resoldered the card back to a bit more cooler 1.35v. But the OC was pathetic.
So I went and got myself 4 80mm fans to better ventilate my cabinet. This is a cheaper alternative to getting a video card cooler. Cost me about Rs.200 and my cabinet now has a total of about 7 fans all strategically placed (cross fingers). My lowly CPU cabinet, which doesn't even deserve to be named (it's a Zebronics Elegance. See?), didn't come with too many fan holes to begin with. But it has two extra holes now thanks to an old screwdriver and a good hammer hand. There was another problem that I failed to see; there's no place to screw-in the fans! That's when i came across double-sided foam. Great stuff this. I bought quite a few rolls of this thing after I saw how good it held. Now I've got four fans stuck-on rather than screwed in. I think the foam also dampens most of the vibration because you won't be able to tell by hearing that about seven 80mm fans are coursing air through my case even when you stand right next to it. I've set them up as 3 intakes and 3 exhausts. The 7th fan blows air across the video card's cooler. The air flow is further controlled by chart paper cutouts which are, you guessed it, strategically placed. I even made a cpu shroud out of chart paper.
Notice the two newly fangled holes? The top hole, as you can see is covered by an exhausting fan and the one on the bottom right is used as an intake hole by a fan inside the case. I had an old epson printer paper tray like thing made of plastic. I took it off in this photo to show the fan inside but I kinda stick it on the fan to keep things from falling into it.
Notice the chart paper shroud-like covering on the bottom-left fan? That is to keep the exhaust from "polluting" the two intake fans next to it:
Feel like throwing up? It doesn't look this bad in person, believe me. The main thing to notice here is the CPU shroud, the video card shroud (below) and the intake fan stuck onto the side of the hard disks.
And here's the ghetto "cpu shroud". This is designed so that the cpu gets completely fresh air directly from the outside via the top side fan. This is so because the cpu cooler is surrounded by exhaust fans (the rear 80mm exhaust fan and the SMPS 120mm exhaust fan).
Right now, my cabinet is a mess. Ok, messier than before. Here's some internal shots:
A sound cooling, this. Yep, that's two fans stuck on the back side of a Creative Live! sound card. Crazy, but my case is not very roomy. The video card shroud is, again, ghetto style.
Here's a view inside the shroud. Double sided foam tape FTMFW!
Notice the tiny loop of red wire on top of the card? That's my old 0.2v volt mod. In my recent mods, I use only a single strand of copper wire when connecting farther solder points (solder doesn't stick to pcb, only to metal). The reason is that, as I found out the heart-stopping way, the copper wire can leverage enough stress onto the solder point on that PCB that it could pry it off along with a strand of the silver trace connected to it! Remember the three mods? Fortunately for me, only the first mod will not work now.
So, I went and did the second mod. Of course, it meant a lot of desoldering and resoldering, which comes with it's own ton of risks, but hey, you learn. So, I guess that's it on my first hard mod. Presently, I am sticking with the 1.5v vmod and the temps are 60°C idle and 83°C load. Bless the approaching winter season, my temperatures presently are 56°C idle and 80°C load. I can only hope the temps will reduce a bit more. Cold climates are always welcome in Chennai. For a more long term cooling, I am currently looking for a very good video card cooler to buy. Like, at least a Zalman VF900cu. But they don't seem to be available in India. There's probably a few available for second hand purchase from an uber geek that's planning for next upgrade since yesterday. And, hopefully, I can get a good deal on it. Perhaps not in India.
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