VCore mod for reducing VCore possible?

[xtremetheme]

Ok, here are the facts. I want to build a htpc, using my old p4 cpu.
It will be in a microatx case using obviously a microatx board. :p:

That means no chance to change VCore using BIOS. But i want it to run on low VCore for better cooling.

There are lot of vmods telling the voltage regulator "omg cpu has not enough vcore give it more!!", so VCore gets up.

My question is, if that is possible, isnt it also possible to reduce the VCore with a mod?

And the board i use is this :http://www.aopen.nl/products/mb/MX46-800N.htm
Maybe some experienced person can give me tips how to spot the voltage regualtor and VCore reading point.


:)

[NiLUS]

Usually pots in VR are linked between FB and gnd.
I think you have to do the same think but between FB ad vout.

Find the datasheet of your VR... you can see there how you have to do.

[xtremetheme]

Thx for answer, i finally found my VR.
This SOB is hiding under the retention module. :p:
http://img33.imageshack.us/my.php?loc=img33&image=vr.jpg

The chip seems to be SC2643VXTS.
I found the datasheet on the manufacterer homepage.
http://www.semtech.com/products/products_line_moreinfo.asp?ProductID=804

Chip connectors are this:
http://img36.imageshack.us/my.php?loc=img36&image=vrchip.jpg

You say i need to connect the FB and the VOut, but which OUT to use?
Sorry im a newb at this.

If i understand we get then additional V from the Vout into the FB, making him think the VCore is too high so he must lower.

But then the VOut will get lower, meaning we get less V on FB, so the chip will raise again, wont the VCore then go up and down and up and down all time :confused:

Cant i take some steady V Source like VCC and connect it to the FB?

And i dont know which variable resistor to use.
I think i will need a high one between VCC and FB, so i block out the VCC complety by default and get +0V on FB.

Then i lower the resistence of the poti so i get slowly more +V on FB, which makes the VCore go down a bit.

How do i calculate which Ohm will completly block out the VCC?

[xtremetheme]

Ok i now looked into datasheet and it states that typical input for VCC is 12V and 10mA, to have a result of 0V on the other side i calculate 12 : 0.01 = 1200Ohm Resistor i need.
So ill try to get my hands on a 2k Ohm variable resistor and use it for this mod.

[LardArse]

You could try increasing the resistance on pin 7 by removing the original resistor connected with pin 7 and put in a VR and increase the resistance from the VR.

[enzoR]

instead of lowering the voltage on FB ( fb to ground) we have to increase it so we have to use FB to 3.3v rail through a pot. right?

[xtremetheme]

Originally posted by LardArse
You could try increasing the resistance on pin 7 by removing the original resistor connected with pin 7 and put in a VR and increase the resistance from the VR.

Hey thats also a good idea. :)
Problem it seems not so easy to get undone.


Originally posted by enzoR

instead of lowering the voltage on FB ( fb to ground) we have to increase it so we have to use FB to 3.3v rail through a pot. right?

That is my plan, but using 12V instead of 3.3V, because a 12V source is right at the chip.
I have no idea if using 3.3V would be better, i dont know if theres 3.3V in near where i could grab from.

[enzoR]

12v is also fine. you just have to use a very high resistance

[xtremetheme]

Well i did the Mod to a MicroATX P3 board and it worked, i can now run my p3 533 @ 1.1V.

But the one on the p4 board doesnt work, the VCore stays the same if i adjust the trimmer, however after a certain point it doesnt boot anymore. :confused:

Maybe i have to mod more then the Feedback pin?
Anybody know what the GNDSEN (Groundsense) is good for?
http://img12.exs.cx/my.php?loc=img12&image=Zwischenablage012.gif

[enzoR]

you have to put a resistor in between the trace to the pin and you have to add voltage after the resistor.

[xtremetheme]

You mean the GNDSEN pin?
Hmm problem i dont see a trace coming out from the pin.

[dTTd]

This migth sound kind of noobish...
But aren't all those VID# , what selects de cpu voltage?
If so, groudind VID0 and and conecting all the others shoud give a 1.1v output voltage (0111= 1,1v):rolleyes:

ps: sorry if bad English...