ECS L7S7A2 SiS 746 Vcore and Vmem Mod Guide
ECS L7S7A2 VCORE AND VMEM MOD GUIDE (Discuss)
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 cannot be held responsible for any damage that may occur.
There are two stages of doing a Vcore modification. Apply mod #1 to achieve a maximum Vcore of 1.94V. If you need more, also apply the mod #2 to get a maximum of appr. 1.98V. Unfortunately, the internal protection of the voltage regulator IC will cut out anywhere between 1.96V and 2.0V so you may not be able to increase the voltage as high as you would like.
VCORE MOD #1:
The L7S7A2 uses a 2-phase power supply for the CPU that is controlled by a Richtek RT9237 IC. That chip has direct input pins that read the voltage coding that is set by the L11 bridges (AthlonXP) on the CPU itself (VID0-4). The idea is to trick the Richtek IC into thinking the CPU has a default voltage of 1.85V simply by shortening all the input pins (1-5) of the Richtek IC. Adding the 5% increase from the BIOS gives a maximum core voltage of 1.94V after the modification. That should be enough for most users that use AthlonXP CPU's.
Locate the Richtek IC between the CPU socket and the PS/2 ports. Pin 1 is marked with a dot on the chip. Take an electronic soldering iron and use fine solder to connect all the first 5 pins (1,2,3,4,5) together as illustrated in Fig.1 below. If you want a removeable modification, you can use SMD clips (as found in good electronic shops) that are connected together with a wire and carefully hook them under the pins of the IC.
-If you have an Athlon XP2400+ or any other CPU with a default voltage of 1.65V, it is enough to just connect pins 1 and 2 of the Richtek IC together.
Fig.1: Connect Pins 1 to 5 together for a Vcore of max. 1.94V.
VCORE MOD #2:
To get the last extra bit before the over-voltage protection of the Richtek IC activates, the amount by which the BIOS Vcore settings influences the voltage can be increased. Usually the BIOS allows for Normal, +1%, +3% and +5%. This is achieved by 2 resistors that are connected to the FB (feedback) line of the regulator IC. The BIOS has 4 settings and it controls these by switching the two resitors on and off. If one of those resistors is modified, the resulting Vcore can be influenced. The overall maximum Vcore achievable is anywhere between 1.98V and 2V. Remember that this 2nd mod is not easy to adjust since the voltage gets very close to the over-voltage trip point of the regulator IC which will instantly shut down the CPU. In the interest of safety, this protection mechanism should not be maipulated.
Prepare a 200k Ohm variable resistor with 2 wires soldered to it. Make sure it is set to 200k Ohm between those wires. Locate the IC 7407 next to the Richtek IC and solder one of the wires to Pin 2 (Pin 1 is the pin nearest to Pin 1 of the Richtek IC). Solder the other wire to the resistor marked in Fig.2. Make sure that the variable resistor is secured and does not cause any shorts.
-Before you do the mod, set the Vcore in the BIOS to "Normal"
-After you have finished the mod, go back into the BIOS and set Vcore to +5%. If the screen goes black, remove the power and retry, this time set the Vcore to 1% in the BIOS.
-Check the voltage in the BIOS ("Hardware Monitor Setup") and gently adjust the variable resistor to the desired voltage. If the screen goes black, the over-voltage protection has activated and you need to reduce the voltage setting until the board reboots by itself. On my L7S7A2 that is around 1.984 V. To ensure stable operation, reduce the voltage further to stay away from the "trip off" point.
-You need a strong PSU to push the L7S7A2 to its limits. If the PSU is too weak on the 5V rail, you will get sudden reboots and crashes.
Fig.2: Connect the 2 points
with a 200k Ohm variable resistor,
The "Normal" voltage on the L7S7A2 is 2.6V. This can be increased in the BIOS by 3.5% (2.69V). The circuit that controls the voltage (around the OP-Amp LM324) can be modified with one resistor to give a much higher VMEM. I suggest to stay below 3.0V to keep the memory from failing prematurely.
Prepare a 4.7k Ohm variable resistor with 2 wires soldered to it. Make sure it is set to 4.7k Ohm between those wires. Locate the IC LM324 between the Southbridge and the front panel connector. Solder the wires to the connection points marked in Fig.3. Make sure that the variable resistor is secured and does not cause any shorts.
-If the value of that variable resistor is set to 1k Ohm (or you use a fixed 1k Ohm resistor) you will get appr. 2.9V Vmem with the BIOS set to "Normal".
-Carefully adjust Vmem and monitor the progress in the BIOS "Hardware Monitor Setup" until you reach the desired value.
Fig.3: Connect the 2
points with a 4.7k Ohm variable resistor,
I hope these mods help you to achieve the speed or stability you aimed for. Keep in mind that you need extra cooling for the CPU, the memory and the mainboard voltage regulator circuit. All these components will generate considerably more heat than before.
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