VCore and VMem Mod for
the ECS 755-A(2)
Killeroy 31 Jan 2004
NOTE: This MOD involves changes to your HW
that will void your warranty! Please follow the proper procedures for handling
electronic components. You do this on your own risk. The author or this site
cannot be held responsible for any damage that may occur.
The ECS 755-A(2) uses a Semtech SC2643 voltage controller that drives the
2-phase CPU power supply. The maximum voltage for the Athlon64 is 1.55 V. This
default voltage is set on the fly by the CPU and can be changed either in the
Bios (use the modded Bios) or via certain Windows applications.
The SC2643 has a sense input that will calibrate the ground level for that
voltage. This input is usually connected to a ground plane near the CPU. This
calibration can be manipulated to make the SC2643 "think" the ground level at
the CPU is higher than it actually is which causes it to raise the core voltage
Fig. 1 shows what needs to be done.
-Locate the SC2643 which is near the 12V ATX connector.
-Remove the 0 Ohm resistor which is marked within the circle.
-Solder 2 wires to the two empty solder pads.
-Connect the wires to a 470 Ohm Potentiometer/Trimmer such that 1 wire is
soldered to one end and the other wire to the remaining 2 contacts (This is
important!). Set it to 0 Ohm.
Fig. 1: Ensure to connect the 470 Ohm Potentiometer/Trimmer as illustrated. Set
it to 0 Ohm before you turn on the machine!
-Make sure the connections are perfect. If there is a fault and the circuit is
open when you power up the machine, Vcore will go sky-high and damage will occur
to the CPU and the mainboard.
-At 0 Ohm, there will be no increase in Vcore. At 1/2 setting, there will be
roughly a .1 - .2 Volt increase.
-Be careful, the Athlon64 does not tolerate high voltages! Anything above 1.7
Volt will be dangerous to the CPU and the mainboard power supply circuit. AMD
rates 1.65V as the maximum.
-A cooling fan for the mainboard power supply circuit is highly recommended to
cool the caps and the power transistors near the 12V ATX connector.
The memory voltage can be set from 2.5 to 2.65 Volt within the Bios. This
voltage powers the DDR memory as well as the memory controller interface of the
Athlon64 CPU itself. AMD rates 2.9V as the maximum.
This voltage is regulated by a LM324 Op-Amp which can be set to discrete
voltages through Bios control. This mod will allow an increase of all these
Fig. 2 shows what to do:
-Remove the CPU retention frame.
-Locate the LM324 near the Lan port.
-Solder 2 wires to a) the SMD resistor near the LM324 and b) to the unused
ground connection near the Lan port.
-Connect these 2 wires to a 4.7 kOhm variable resistor which you set to 4.7 kOhm.
Fig. 2: Connect at 4.7 kOhm variable resistor as shown. Set it to 4.7 kOhm
-After putting it all back together, you will already see some increase in Vmem.
-Be careful not to exceed 2.9 V as this is the absolute maximum rating for the
Athlon64 memory controller.