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Vmod questions - - different look at memory


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Old 25-04-2009, 12:01 PM   #1
s e r e n i t y
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Vmod questions

Hey guys,

Does anyone know of any good threads where I can learn a bit more about GPU, mobo vmods?

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Old 25-04-2009, 01:30 PM   #2
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Your best bet is to try and get help voltmodding, say, a cheap video card and learn in the process. Usually it involves finding the gpu and memory voltage regulators, and the chips that control them. Then you find datasheets for the controller chips, and from there you know which pins to mod. It's a lot easier than it sounds, and after doing it a few times it becomes pretty easy

(Just make sure you practice on cheap hardware first, as the solder points are always pretty small)
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Old 25-04-2009, 06:48 PM   #3
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Alright, I have found a little write up on vmodding for anyone interested.

Alright, this guide is for those who would like to vmod their graphics cards/mobos but don't know where to begin. This method works in most cases, but sometimes there are obstacles like overvolt protection etc... so try it at your own risk. This mod will void your warranty. If anyone has suggestions please say so and I'll update the guide.

Materials needed:
- Multimeter

- 2B pencil
- 2x variable resistors, some wire, and a soldering iron w/ solder

1. First, find the voltage regulator chips. On graphics cards these are usually on the back, and on mobo's look near the component you want to mod - e.g. for a vcore mod look near the CPU. These look like black rectangles with lots of silver pins sticking out the side.
On top of these chips you will find codes such as RT9259, ISL6522, etc. Look for codes beginning with the letters HIP, SC, LM, RT, ISL and ADP. Google these codes, and you should be able to find PDF product sheets - if not, try a different chip. The correct chips usually have the title "Synchronous Buck PWM Controller" or something to this effect. If you're modding your gfx card, there will be one for vgpu and one for vmem (often both use the same code), or sometimes there is one chip which controls both, but I'll get to that in a sec.

2. Once the correct chips have been located, look through the product sheet for a pin layout diagram. Locate the FB (feedback) pin. By reducing the resistance between this pin and ground, the relevant voltage (vgpu, vcore, vmem, etc.) will increase. Sometimes there are FB and FB2 pins; in this case one controls vgpu and the other vmem. Anyway, you can do the mod in one of two ways:

a) Find a resistor connected between the FB pin and ground, and shade this resistor with your pencil (this reduces the resistance).


b) Attach a variable resistor between the FB pin and ground, and reduce the resistance by adjusting the dial.

The choice is yours. VR mods allow greater increases in voltage and give better granularity, but you need some soldering skills to be able to attach wire to those tiny pins. Also there's the problem of where to put the wretched things so they don't fall onto your card and short it out.

3. a) If you chose the pencil mod, get your multimeter ready, and measure the resistance between the FB pin and some nearby resistors (with computer turned off). Once you get a reading of 0, this confirms that the two points are connected. Now measure the resistance between the opposite end of this resistor and ground. If you get 0 again, this is your magic resistor. Shade it and voltage should increase.

b) For the VR mod, measure the resistance between the FB pin and ground. Multiply this value by 20, and get a VR with the resultant value (or a little higher). e.g. If the resistance is 624 ohms, 20x624=12480, so get a 15k ohm VR. Now attach the VR between the FB pin and ground with your soldering iron and some wire.
Set the VR's to maximum resistance, and gradually decrease it for increased voltage.

Please Note: Voltage adjustments should always be made with the power turned off to avoid damaging components.

If you're doing a gfx card mod, you'll need to figure out which chip controls vgpu and which controls vmem. If both chips have the same code, just measure the resistance between the FB pin and ground - whichever has the greater resistance will most likely be the vgpu mod, since gpu voltage is lower than vmem voltage most of the time. If the chips have different codes, just do the mod and figure it out after - more gpu voltage allows greater gpu clock speeds, and vice versa.

Now for the voltage measurement points. On mobo's, just use speedfan or BIOS to monitor the voltage. On gfx cards, look for some inductors on the front of the card - these are usually donut shaped with copper wire wrapped around them. Look underneath the card for the two inductor pins, and measure the voltage between each pin and ground. If you get a value close to what the vgpu/vmem should be, this is your measurement point. Generally the inductors are close to the voltage regulator chips, and so you can determine which chip controls vgpu and which controls vmem by looking at the nearby inductor voltage.

If the inductors don't give you the correct voltages, you can use a formula to figure it out:

v(new) = v(stock) x [ r(stock) / r(new) ]

The resistances are measured between the FB pin and ground. To find the stock voltage use google.

If you want to check the maximum voltage for your RAM, google the codes which are on the RAM chips, and look through the product sheet for a 'maximum safe voltage' rating.

Well that's all I can think of for now. To see this method in action, have a look at the 7600GS volt-mod guide, which uses the variable resistors. Good luck and enjoy your volt-mods.
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