P4Gd1/P4gpl-x variable vdimm mod

There is a known mod that feeds RAM directly from 3.3V line. So, RAM voltage = PSU 3.3V line voltage. Is it possible to change RAM voltage without changing 3.3V PSU line? Does anyone know what type of resistor do I need between those points to change RAM voltage? If not then how low can 3.3V line be? For example, 2.9V ok or not? The problem is that I can only use RAM that likes high voltage. Or I should use some switch to enable/disable mod.

http://home.no.net/comerade/pc/p4gd1_3,3v-vdimm.jpg

Can you post any pictures of the DIMM slot area on the board please.

Here you go, front and back

I've found a thread that I posted in over at VRforums, but the thread died before I could get the voltage readings for the mod.

here is the thread

Can someone check the voltages at the points I've marked here

I measured voltages on the modded board already. PSU 3.3 line was around 3.14V. If I increase it to say 3.4V then all voltages at green points also increase.

From the top to bottom,
1st chip: purple 12.11, green 3.14
2nd chip: purple 2.99, green 3.11
3rd chip: purple 2.99, green 3.09
Last chip: left both 0.8, right 10.7 and 4.83

what? with a 3.3v line set to 3.4v you only get 3.14v (real) to the dimms?
that's pathetic. even less then with the normal vdimm mod (connecting pins
on that lm-chip) on the p4p800-se.
isn't there a straight 3.3v to vdimm pins mod like kyosen did with some other
boards? the pic you posted way at the top looks somewhat different. i used
to think you connect the 3.3v spot on the 20pin (or 24pin) psu-plug straight
to pin x off the dimmslots, not to a point somewhat off the socket (that may
be connected to the dimm-sockets via some resistors, etc etc...) ?

^^^ this is me thinking, nothing to be taken at face value.. (just in case)

example pic of what i mean.. some aopen board (i855gmem lfes iirc):

No,

Quote:

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Originally Posted by kiwi

If I increase it to say 3.4V then all voltages at green points also increase

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When PSU line is @3.4V then RAM voltage (and readings at green points) is approximately the same i.e. around 3.4V :D I have tested it up to 3.6V

But as I said I can regulate voltage only on my PSU :(

OK volt measured on a P4GD1 set to 2.90V in bios running 2 sticks of RAM

From this image the following voltages were measured with reference to ground -

For MOSFETS starting with top most MOSFET

Green pin - 3.41v
Pink pin - 11.86v

Green pin - 3.06v
Pink pin - 4.61v

Green pin - 2.73v
Pink pin - 4.27v

IC starting top left going anti clockwise

Pin 1 - 3.38v
Pin 7 - 4.10V
Pin 8 - 4.51v
Pin 14 - 10.37v


Hope this helps

JB

How can there be such difference between P4Gd1 and P4gpl-x? PCB is almost the same. Maybe because my board's been modded already? :rolleyes:

Dunno, tho I would expect the mod to have a big effect. Gues we'll have to wait till someone else give in their readings!

Done a bit more testing, discovered with MOSFET ouputs the vdimm voltage :

http://img360.imageshack.us/img360/2...d1vdimm4xq.png

Hope this is of some use to you all :)

Can someone check the resistance between the pink pin on the Vdimm MOSFET (the MOSFET in Johnny Bravo's post above this post), and pin 7 and pin 8 on the LM324.

Edit: check resistance with the power off

1.5K for both tho I don't trust the reading, slow to settle out, I suspect a capacitance may be charging up somewhere on the line. These readings mean anything to you?

Actually got the data sheet and see notch, Pin 7 has infinite resistance and pin 8 is reading 1.513Kohm atm

yeah pins 5 &6 are tied to ground so pin seven is out of the running

Quote:

---

Originally Posted by Johnny Bravo

Actually got the data sheet and see notch, Pin 7 has infinite resistance and pin 8 is reading 1.513Kohm atm

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Are you checking the resistance between the pin on the LM324 and ground, or between the LM324 pin and the pink MOSFET pin?

between MOSFET and Pin

hmm, I get 2.99K (pin 7). Nothing @ pin 8. Probably I should remove the mod and measure then.

http://www.xtremesystems.org/forums/...id=40162&stc=1

connect a 50k VR between pin 9 and ground. Decrease resistance to increase voltage. I've marked pin 9 on the attached picture :)

Note: XS owners and members will not be liable for any damage caused to you or your hardware, neither can be liable for any breach of the warranty.

will tell u how its goes some time after 5 tomorrow Persivore, got to take labs in the afternoon so won't be able to get anywhere near the board till I get back home.

vdimm mod confirmed! Measured upto 3.3v fully adjustable so far :-

http://img507.imageshack.us/img507/86/imgp13515ai.jpg

nice! i'm sure many people will be happy. good work as always guys, good work

Thanks a lot :) Good job Persivore and Johnny Bravo

:toast:

We may not be finished here guys, was doign some testing today and it seems that the max is ~3.33v regardless of how low a resistance goes between these two pins. Unfortunatly my BIOS became bored with living and now I have to get the chip reprogrammed...*sigh*

If anyone else has done this mod and can get higher vdimm please report in here!!!

Cheers

JB

The max Vdimm will be limited by the 3.3v line. You will need to have the 3.3v line about 0.2v higher than Vdimm :)