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The Simple & Concise 7900GT Voltmod Tutorial

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Originally posted by: crazylegs
Its some of the other components that get MEGA HOT... thing they called mofats or something... anyway some of the other parts to do with MEM but not actual MEM chips they get hot as HELL... if i had any spare HS i would pop some at random places all over the card! 😀

PS. my temps have only been taken using finger on various places when the card is OCed high and artifact testing! but trust me they some bits get way HOT!
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It's MOSFET. Metal Oxide Semiconductor Effect Transistor and yeah they do get very hot. The 7900GTX cooler for instance, actually cools the power MOSFETs.
 
Originally posted by: dman918
Makes me wonder if a HS on those uber hot chips would make a difference for me.
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Some power MOSFETS get soldered directly to the printed circuit board (PCB) in such a way that the body of the transistor (metallic) is actually soldered. That arrangement lets the transistor use the PCB as a heat spreader. To cool such a device, you would want to cool the PCB. So, you would want to have lots of air circulation around the PCB.
Placing a heat sink on such a transistor can actually block air reaching the PCB and effectively degrade the cooling.

I am not sure about this specific device you are considering. I just wanted to point out that attaching a heat sink to a semiconductor device is not always the right thing to do!
 
I just want to try to get better than a 625/1700 OC at 1.4v if possible. I am wondering if I am doing anything wrong, but there isn't a heat issue, so maybe it is just a limitation of my board. :shrugs:

Oh BTW, those multimeters at Harbor Freight are $2.99 in-store as well. Got mine for like $3.20 with tax!!!
 
Originally posted by: Navid
I am not sure about this specific device you are considering. I just wanted to point out that attaching a heat sink to a semiconductor device is not always the right thing to do!
Click to expand...

On the 7900GTX, the stock cooler's heatsink is built to cool the MOSFETs as well though the heatsink itself doesn't make direct contact.
 
Originally posted by: 1Dark1Sharigan1
Originally posted by: Muhadib
I like to get every single drop of performance I can get away with. Why not? <shrug>
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You could damage the RAM chips since they don't throttle.
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Could, meaning you don't take the proper steps to ensure that you don't. Thats why I added the "I can get away with" part in my last post.
 
The reason this thread was removed from sticky is? Oh let me guess...EVGA's signature series is already doing this? And we don't want anyone saving money....do we?
 
OK, as you all know, I have been asking a lot of OC questions. The best OC I can get is 625/1700, and it is bothering me a little. Could it be that the heatsinks supplied with the VF700 is actually hurting the temps of the mem? It seems weird that I seem to have the worst mem OC here. I did reuse these from my old card, but applied new thermal tape in its place.
Thanks!
 
Your mem isn't much of a bottleneck, try lowering a little and you'll see a very small change, the change for increasing it would be smaller.
 
Just quick question about memory voltage. When I play COD2 the vmem goes to about 2.24v, thats safe right? Cause when I'm not gaming it's only ~2.22v. It's nearly impossible to get it right on 2.2v.
 
So, this is the first ive heard of 1.5v not being totally safe via this method... i was planning on doing the 1.55v.. am I going to have issues?
 
Originally posted by: compgeek89
So, this is the first ive heard of 1.5v not being totally safe via this method... i was planning on doing the 1.55v.. am I going to have issues?
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It's all a matter of opionion. Some will say that 1.5 is totally safe. Actually any overvolting would not be safe because any number of things can go wrong. Not that I'm saying it will, because even up to 1.5v it is extreamly unlikely that something will go wrong.

Some people say that the voltage regulators and the mosfets can't handle the additional volts, others say you are shortening the lifespan of the card too much.

1.4v is pretty safe. Seems the voltage regulators and mosfets can handle it ok. And it's what the stock GTX's run at so you don't really have to worry about the die burning because of voltage.

1.5v, again is relatively safe. I think the concern here is more towards the power requirements that put stress on mosfets and other components, and I don't really think it's about the die and increased voltage. 1.5v for me would be the limit.

It's all how your card OC's for you. Ask yourself these questions, How far can I get with 1.4v? If I add .1v to make 1.5v, is the OC that I gain from the added voltage worth it? But I really don't think you'll be needing 1.55v to get a good OC. Let's not go overboard here. 😉
I get 675/1900 out of mine with 1.4v and 2.2v respectively.

Also, don't forget about my question of whether 2.24v is safe for the vmem or not? 🙂
 
Originally posted by: compgeek89
Well, my mem seems to do 925 @ stock as it is. I want 750mhz on my core though.

I dont mind using a heatsink on the mosfets... its these right?
http://img236.imageshack.us/img236/6950/79gtvmodss0om.jpg (not only the circled one, all 3)

edit: entire pic here: http://img210.imageshack.us/img210/2647/79gtvmodss3wn.jpg
Click to expand...

I don't think it's really a matter of how much heat the mosfets produce, but how much voltage they can handle. I'm not really sure on this though. 1.55v does seem high to me, but it's your card and you can do what you want with it I guess.

You have 7900GT's in SLI (much like I do, or did since one crapped out, not because of vmodding). What do you need 750mhz on the core for. Arn't 2 7900GT's @ 675 or thereabouts enough? What res are you gaming at. 675mhz is still faster than most stock GTX speeds.

Maby someone else should comment on this.

Don't forget about memory voltage question 😉
 
I dont know about the mem voltage.

Im going for the world record for 79GTs in 005/06, Im at 15688/9689 with stock voltage, I need 16.5k/10.5k for the WR, I think I can do it @ 750-775.
 
So 100% cannot use pencil to vmod 7900gt? If use conductive pen, will it be able to clean the thing of so the warrenty will not be void or once u vmod, ur card warrenty will be void no matter wat?
 
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