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Vcore Mod For GA-965P-S3 Motherboard Rev 1.0
NOTE: This Vcore Mod is for GA-965P-S3 Motherboard only. The power supply circuit may be different on the other boards in the family.... Check the board layout carefully if your going to try this on another model board.
The GA-965P-S3 has a very nice Vcore range in the BIOS. The problem is the last 3 steps are too big a jump. They are 1.60V, 1.80V, and 2.0V.... We need 1.65V and 1.70V also. So the solution is to add a percentage such that the BIOS can be set to lower voltage settings where there is finer increments.
Here is the PWM circuitry that generates the Vcore. It's stragically placed near to the CPU in order to distribute the Vcore amperage with as little loss as possible. The mod resistor gets soldered between pins 14/15(the're connected together) of the ISL6312 PWM chip, and any ground on the board. Problem is the pins are so small, it's nearly impossible to solder to. The mod resistor is 20K. That will yield a 10% increase in Vcore. So when the BIOS is set for 1.50V, the CPU will be getting 1.65V.... 40K will yield a 5% increase above the BIOS setting...
I haven't been able to find an alternate solder point as yet. Anyone with this board that can identify a good solder point, please add to the topic....
If you do this mod, your doing it at your own risk. The Rebels Haven Computer Forum will not be responsible for damaged systems or components... If your unsure about the mods, I strongly suggest you do not implement them...
-------------------- Too Many Computers,... Too Little Time ..... Damn Phenoms! Posts: 25194 | From: Fire Island, NY | Registered: Feb 2003
Someone asked how I arrived at the final value of the mod resistor for another motherboard, so I decided to add it here also, and here it is. We'll start with some basics. And by the way, this is the way all Switching Regulator voltage mods can be arrived at. The resistor always goes from the feedback (FB) pin to ground. Some motherboards have what is called a "Remote Sense Buffer Amplifier". Then the mod is performed a slightly different way.
The typical Switching Regulator Power Supply schematic for the ISL6312 chip that is used to generate Vcore, looks like this:
Here are the calculations to arrive at the final value for a fixed percentage increase. First we measure the resistance from the feedback (FB) pin, the "minus" pin on our "Error Amp", to ground. This is performed with a Digital Multimeter with the power disconnected and the negative lead of the DMM on ground. Record or note this value. For this motherboard, the value was approximately 2Kohms. This would be "R2" in our following schematic:
The "job" of the Switching Regulation circuitry is to make the "plus" and "minus" inputs of the Error-Amp equal. By reducing "R2", the circuit needs an increase in "Idiv" to make that happen. The circuit does that by increasing the output voltage, "V"....
So, now for a quick, but close, approximation... If for example we want 10% more output voltage, we need to increase "Idiv" by 10%... That is implemented by reducing our "R2" by 10% or adding a resistor in parallel that will then total 10% less resistance. If you do some parallel resistor calculations(product divided by the sum), you will find that to reduce a resistor by 10%, you need a parallel resistor of 10X the value of the resistor your trying to reduce. For a 5% reduction, we use a resistor that is 20X the value your trying to reduce. For 1% increase, we use a resistor of 100X. And it's as simple as that!
So here's a list: 20K --> +10% of set Vcore 40K --> +5% of set Vcore 80K --> +2.5% of set Vcore
Now, many users want to adjust the voltage higher or lower then a fixed resistor would yield. For a 10-20 turn Variable Resistor value, I would suggest a 100X the "R2" value. That way the increase can be adjusted to almost zero. But for this motherboard and this circuit, a 100K or 200K Variable Resistor is just about perfect and gives a slight boost when set to maximum resistance. I used a 20K fixed resistor.
Last thing, set the Vdimm in the BIOS to the lowest it will go before doing any mod. Vdimm should be measured with a DMM to make sure your getting the voltage you want..... Have fun!
-------------------- Too Many Computers,... Too Little Time ..... Damn Phenoms! Posts: 25194 | From: Fire Island, NY | Registered: Feb 2003
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The traces have been identified and the photo updated showing the solder points for the Mod Resistor..... I had bought a Bausch & Lomb Stereo Zoom 4 microscope just for this mod. It is a "surface magnifier" with 3x to 30x magnification. It can go higher magnification with eyepieces, higher then my 10x...
Topic Closed
Damn Phenoms!
![[Big Grin]](biggrin.gif)
