Making your Asus P5WDH (Deluxe) Ready for Conroe: An Illustrative Guide
PART II: Completing the vMCH mod (aka vmodding 101)
brought to you by xtremesystems.org
Introduction and General Disclaimer
Completel ANY modification is at your own risk. This guide is intended to provide direction only and does not constitute ANY responsibility on my or the site's (XS.org) behalf with regarding to possible damage to a) your board, b) yourself, c) ANYTHING. Remember, nobody knows your limitations better than you. Have fun but play safely!
Here's our board again. Conroe installed and waiting. You know how important it is to work cleanly now (at least you should after reading my original guide). I recommend lightly cleaning the working area...in our case...as shown below.
http://www.jpop.com/fcg/DSC02383.JPG
http://www.jpop.com/fcg/DSC02386_A.JPG
Here are our two (2) solder points:
http://www.jpop.com/fcg/DSC02390_A.JPG
I have numbered the pins. Pin 1 starts at the "dot" marker. Then, continuing down the same side of the IC...pin 2, pin 3, etc...when you get to the end, continue counting from the pin directly across from the last on that side....when you get to the end...STOP. This particular IC has 8 pins (SOP-8 package). We will be soldering to
Pin #3 and
Pin #6
If you care to know more about the theory involved in our particular modification...we can cover this more at a later time. Right now just understand that we are forcing the regulated output voltage, in this case the voltage feeding the NB, higher by inserting a manual offset in the circuit feedback loop. The system will work to compensate by increasing the output voltage in response to our handwork. ;)
You can find the PDF datasheet for the RichTek RT9214 (5V/12V Synchronous Buck PWM DC-DC Controller)
here if you care to read more about this particular component. (You're highly encouraged to read.)
First, everything you will need. (I think I forgot to include a single straight razor blade in the pictures.) If you haven't figured it out, yes, that's the part number for the potentiometer from Digi-key there. Please don't everybody PM me asking for the part number.... :rolleyes: For those that have stash or perfer to deal with some other reseller, it's a 25-turn 10K ohm potentiometer.
http://www.jpop.com/fcg/DSC02398.JPG
http://www.jpop.com/fcg/DSC02400.JPG
http://www.jpop.com/fcg/DSC02402.JPG
http://www.jpop.com/fcg/DSC02427.JPG
If you don't deal with
Digi-Key I highly recommend that you check them out. Create a login and order a catalog (FREE). You will get a new one about every quarter or so. Digi-key has just about EVERYTHING you could ever need and great prices, too. Tell them Kris sent you (just kidding, they will have no idea who I am). :p:
OK, turn on your soldering iron now. I don't use anything fancy. I believe it's a 45W Weller. You don't need to crank it up as high as it will go. Go to about 3-4 to start. Really, we don't need more than about 20W of heat. Before we begin soldering there are a couple of things we need to go over. This should be your mantra when working with computer electronics:
1) My hands are my rock, I shall not shake.
2) I shall apply heat no longer than absolutely necessary.
3) I shall act sparingly with my solder, too much and I shall certainly bridge a few pins.
BTW, please, don't let your brand new $275 motherboard be the first thing you solder on. Practice on something else.....please.....pretty please.... :) And if you don't think you can behave and follow the three simple "rules" above, by all means, don't attempt this. Maybe think about finding someone who can help you out...
Step 1: Prepare your potentiometer
Start by turning the set screw on your potentiometer
at least the maximum number of end to end turns in the counter-clockwise direction (we will cover why later). This will ensure that you have reached the maximum value for at least one of the "two internal resistors." Yes, there is only one "resistor bank" inside and only one wiper arm. For the purpose of describing what is happening we will model this system as two resistors as illustrated below.
The object on the left is the IC that we will be soldering to. The red lines will be the wires that we solder in. The object on the right is the potentiometer.
Just remember this:
A + B = 10K ohm ALWAYS (sometimes 10K will be a little off...like 10.3K....this is normal)
What this means is that if B = 5K then A = 10K - 5K = 5K. If we turn the set screw and move the wiper blade A or B will increase (or decrease, depending on the directing of motion of the set screw, clock-wise or counter clock-wise) such that A + B is a constant. If A goes up then B goes down and vice versa....Got it? :cool:
http://www.jpop.com/fcg/vmod.JPG
Now that's all well and good. Except that we just want to insert some parallel resistance from the FB (feedback) line to ground. Any ground will work. We chose Pin #3 of the IC because it's 1) close, 2) easy, 3) did I say close? :p:
The red "x" means that we won't be connecting that leg of the potentiometer. The middle leg is the wiper leg and the two on either side are the other sides of the "A" and "B" resistances that we create by moving the set screw. Not all potentiometer are setup exactly the same that's why I have provide you with a part number. I recommend you buy the same type that I have used in this guide.
Since there is no potential developed across "B" we get no current flow through "B." For all intents and purposes we can model the system as if "B" didn't even exist:
http://www.jpop.com/fcg/vmod2.JPG
http://www.jpop.com/fcg/DSC02409_A.JPG
So, turning the set screw from one maximum to the other makes "A" go from 0 ohms (minimum, a short - a no-no) to 10K ohms (max). Here's what we are really doing to the system. We place "A" as labeled. The second placement of "A" inside of the dashed-line box is the same as that which we show as going straight from Pin #3 to Pin #6. Why? Because all grounds in this picture are the
same, which I have further illustrated by connecting them together with the longer red lines.
http://www.jpop.com/fcg/vmod3.JPG
Why not just insert a resistor and be done with all of this? Simple. We want our modification to be adjustable....hence the use of the potentiometer.
Now that we've established that we only need to two legs all we need to do now is determine
which two legs. Well, we already said that we had to keep the middle leg. Measuring the resistance between the outer two legs is always 10K...remember...A + B = 10K. No matter how we move the set screw the total resistance of the "resistor bank" doesn't change, only the resistance from one end to the tap-off point (the middle leg).
-> Here's how I choose which outer leg to keep. I make a standard convention, such as: clock-wise motion on the set screw is an
increase in voltage (not necessarily an increase in resistance, usually just the opposite...)
-> In this case a decrease in resistance causes an increase in voltage. So, turning the set screw clock-wise should cause the resistance between the legs I chose to go down.
-> Since I want to install the modification at a minimum I have already pre-set the potentiometer by turning counter clock-wise the maximum number of turns. (remember this from before?)
-> That means that since I have already set a maximum from one outer leg to the middle I just need to determine
which outer leg is at a maximum! :D How? Measure with a multimeter from the middle leg to each outer leg separately. One should be ~10K and the other 0K. Yes? If not you have not turned the set screw couter clock-wise enough times.
-> Once again, maximum resistance is minimum increase in voltage. So find that outer leg that measured as a short to the middle leg and clip it off!
Here's what you should end up with:
Note: I also cut the other two legs a little shorter, we don't need all that length.
http://www.jpop.com/fcg/DSC02414.JPG
Another way to look at it:
http://www.jpop.com/fcg/vmod4.JPG
See the legs labeled? "CW" means that clock-wise set screw motion moves the wiper in that direction. We moved it "CCW" so the wiper moved to "1." So the middle to "1" was a short and "3" to the middle ("2") was a maximum. So we cut of "1" since we want a maximum for CCW motion since CW motion from this point lowers resistance (from a maximum) from 3 to the middle leg ("2"). And lowering resistance is an increase in voltage since the FB pin on the IC uses a pre-amplified inverting input! If you don't like this method use the method descrived above. :D
In the end, it really doesn't matter which way you turn the set screw to change the voltage. I strongly recommend that you have a convention so that you don't start cranking up the voltage by accident thinking you are lowering. Since raising and lower the resistance may have different responses with different PWM controller ICs you will need to think through this process every time. Be careful. Installing a potentiometer with the legs shorted can kill a board if a minimum resistance on the feedback pin sets a maximum output voltage...BOOM. :(
Step 2: Prepare your wires
I use
small wire. I think 28 or 30 gauge. Black is my favorite color (disappears the best) but red is all I have. Onward!
Cut off a couple of short lengths...think like 1" or so. Generally, the shorter the better. If you have to mount the potentiometer farther from the modification site then you will obviously need more wire.
http://www.jpop.com/fcg/DSC02406.JPG
http://www.jpop.com/fcg/DSC02420.JPG
Now using your flat straight razor strip a small section from the ends of each wire. If you have a wire stripper that can handle this guage then by all means go for it! (wow) When you are using the razor you should be making more of a scraping motion as you turn the wire....if you press down too hard you will probably just cut the wire outright. Here's what it should look like when done as well as a short with one done and one remaining:
http://www.jpop.com/fcg/DSC02421.JPG
http://www.jpop.com/fcg/DSC02424.JPG
Step 3: Solder everything together!
We'll start by soldering the wires to Pin #3 and Pin #6 on the IC. Remember, don't use any more heat than you absolutely need to and don't hold the soldering iron directly on the IC legs an longer than necessary (2-3 seconds maximum.) Just remove the iron in between soldering attempts to allow the IC to cool. High heat for too long = damage. Heat head for soldering in short bursts = fine and dandy.
"Tinning" your soldering iron head will help. Do this by allowing the solder to coat the tip of the iron. Allow a little to accumulate so that you can move this to the leg of the IC you are working on. "Tin" the leg as well as the wire end that you will be join it. Work clean. If the heat causes the flux in the solder to burn and make a dark residue remove this from the iron tip by quickly running it across the wet sponge you have nearby.
Once you have both wires attached they should be secure enough that you can raise the board off your work surface by lifting with the wire you just soldered to either IC leg.
http://www.jpop.com/fcg/DSC02433.JPG
-> Not my best job there but this is some small stuff! ;)
Once the wires are soldered in we simply line up the other end with a leg of the potentiometer. Which one doesn't matter.
http://www.jpop.com/fcg/DSC02437.JPG
The apply a blob of solder (good thing that looks don't matter in this case!):
http://www.jpop.com/fcg/DSC02441.JPG
And repeat:
http://www.jpop.com/fcg/DSC02444.JPG
http://www.jpop.com/fcg/DSC02446.JPG
Now simply move the wires so that they are positioned as you like. Don't use too much force. Don't want to break a line. Just get them out of the way and in a safe place:
http://www.jpop.com/fcg/DSC02455.JPG
http://www.jpop.com/fcg/DSC02459.JPG
Last step is to use a small drop of super-glue to firm attach the potentiometer to the board. This is about the only real part of the mod that makes it non-removable. Of course, if you want to be able to remove it later to sell the board to someone that want it stock you can always use something a little less permanent when securing the pot in place.
When you boot the board you should see very little change in vMCH (via BIOS) since the potentiometer is set to maximum resistance. I recommend that you set the BIOS vMCH to 1.65 before you adjust up. This way you can't set 1.8v when BIOS is at default and then later send 2.1v through you NB when you pick 1.65v in BIOS.....I've seen worse....lol.
If you care to learn more about how the NB/MCH responds to voltage with this board this would be a good place to start!:
Asus P5W DH Deluxe MCH Overclocking Response
-FCG
:toast: