Hi there,
recently I sucessfully unlocked, underclocked and undervoltaged an
XP2400+ on A7V333 (see other post).
How can I undervoltage the CPU on my A7N8X?
(old deluxe version and/or -E deluxe)
I tryed on the -E with BIOS 1008 and I can overvoltage it to the
lightning point, but not a bit under the supposed 1.65V.
On A7V333 I fidled aroud with VID settings and could go down to 1.1V.
Any Ideas?
read you!
KALLE
P.S. YES, underclocking DOES make sense in some cases!
I can think of three ways.
1) Find a modified BIOS, that offers menus with more options.
There is an Uber BIOS for the A7N8X, but I don't know if
the voltage menu is expanded or not. Asus seems to have a
policy of not allowing undervolting, and that is why this
is so much work.
2) Make an analog modification to the Vcore voltage regulator.
I think the L6917BD datasheet is here (assuming that is the
regulator your board has):
http://www.st.com/stonline/books/pdf/docs/8162.pdf
Connect a resistor between pin 9 (FB) and a regulated supply
like the +3.3V from the power supply. The wiring must use
short wires, to avoid coupling noise into the circuit. You
will need an assortment of resistors. On page 16 of the data
sheet is a reference schematic, and you could start by
measuring the equivalent resistor to R9 on your motherboard.
(Of course, it won't be labelled R9 on the motherboard, but
will have some other number). I would start with a resistor
of say 10x the measured value of R9, to make your connection
from FB to +3.3V with the resistor, then reduce the resistance
depending on how much change you get with that starting value.
+3.3
|
L6917BD |
____ Resistor
| 10x "R9" measured
|9 |
|---------------+
|
|
----
On the one hand, this is a risky mod, because of making a
mistake and having the voltage rise too high, damaging the
processor and/or Northbridge. On the other hand, it is
relatively easy to solder two fine wires to the board, with
the resistor suspended by the wires. Use fine wire, as this
reduces the tugging stresses on the copper pads. Do not
solder a resistor directly (if using a leaded 1/8W resistor
for example). The fine wire (like a wire wrap wire 30 gauge)
decouples the stresses from the component.
3) Make a digital modification. There are five VID pins. A
typical implementation consists of the CPU VID pins being
connected to some GPIO pins on the Super I/O chip, and also
to the VID on the voltage regulator. The path between the
CPU and the GPIO is separated by resistors, making the
drive from the CPU weak. If the GPIO is in input mode, the
Super I/O can be used to read the VID code coming from the
processor, so the BIOS knows what the processor wants. If
the GPIO doesn't drive the lines, the CPU gets to determine
the VID logic levels, via the weak resistors. If instead,
the BIOS wishes to enforce a particular set of logic levels
on the five signals, it enables the GPIO to drive out. The
GPIO drive is stronger than the CPU drive, because of the
series resistors, so the GPIO value wins.
The easiest mod, would be to solder five wires to solid
logic levels like the +3.3V rail or ground. But, this could
damage the GPIO if it is driving at the same time. Parts
vary as to how much overload they can take - some GPIO
pins could take an indefinite overdrive, whereas others
are only rated for abuse of at most one pin at a time.
That is the reason that I recommended prying up the five
VID pins on the voltage regulator to "LarsJ", a person who
recently modified a A7V8X for undervolting. With the pins
lifted off the board slightly, so a mylar sheet can be slid
underneath them (after the soldering is finished) for
insulation, you simply leave the pins open circuit where
you want a logic 1 and ground the pins where you want a
logic 0. The VID pins have internal weak pullups, and that
is why an open pin goes to logic 1 voltage on its own.
(Click complete thread)
http://groups.google.com/[email protected]
Be careful while soldering, as it is easy to tear the copper
foil on the motherboard, by applying too much force with the
soldering iron. Desoldering requires the soldered joint
to be dry, before you can attempt to pry the pin up. This is
pretty difficult to achieve, without practicing your skills
on a dead motherboard first.
So, I would start by looking for info on modded BIOS, and then
use a hardware mod, if the modded BIOS doesn't have the needed
VID values in it. Even writing some software to program the
Super I/O pins, after the system is booted, could be done,
if you have info on where in the memory map it is located.
That assumes the BIOS code is not constantly refreshing the
value in the register
HTH,
Paul
