ASRock 939Dual-SATA2 VCore & VDimm Voltmods

Introduction

The ASRock 939Dual-SATA2 is a great value oriented board for AMD Socket939. It has both a native PCI-E x16 and an AGP 8x slot.
Unfortunately the BIOS is lacking overclocking options.

With an AMD Venice CPU the maximum CPU voltage available is 1.450V, definitely not enough for some serious overclocking.

Settings for memory voltage are even more limited: "Standard" (2.6V) and "High" (2.7V) just doesn't cut it.

Another issue is that with all official BIOSes you will have great trouble overclocking beyond 275 MHz HTT (v1.40 was the latest when this article was written).

OCWorkbench has released two tweaked BIOS files which fix the 275 MHz clock issues.

VCore Mod

ST Microelectronics' L6711 voltage controller can deliver up to 1.550V to the CPU. The output voltage is selected via VID code. For example if the VID code is 00110, the resulting voltage is 1.400V.

The marked solder pads have the "signal" on the left and ground on the right. So if you bridge one of these, the VID code will always be 0, no matter what the CPU sets.

The following table lists all possible VID code combinations.


For this mod we will change the VID4 code to always return '0'. This is done by bridging the VID4 solder pads with a solder blob or conductive paint.



Now, if the BIOS sets a voltage of 1.100V (VID Code 10010), the resulting VID code would be 00010, which is 1.500V.

With the voltmod done, any voltages listed in the table above that have a 1 for VID4 will get a 0.4V bump. The list in the BIOS will be the same, but the actual voltage is different.

So if you set 1.150V in the BIOS the real output voltage will be 1.550V, if you set 1.125V it's 1.525V, 1.100V is 1.500V an so on.

Voltages which already have a 0 for VID4 remain unaffected.

VDimm Mod

Depending on your needs there are several ways to increase the memory voltage.

3.20V

The red solder pad carries about 3.20V. If you bridge this solder pad to the VDIMM solder pad with a wire, you will directly feed the 3.20V into your memory.

3.30V

If you need more voltage, you can route an orange wire (3.3V) from your ATX Power Connector and connect it directly to the solder pad.
This mod is even more useful if you have a PSU with adjustable 3.3V rail, because changing the 3.3V rail will also change your memory voltage. With two memory modules about 3.5A will run through your wire during load, so make sure you do not use a too thin wire.

Variable Voltage

The BIOS setting VDimm controls the transistor "1". If the voltage in the BIOS is set to Normal, the transistor is closed. When set to High, the transistor is open and will drop the voltage seen on Pin 9 of the LM324. The resistance of resistor "2" will determine how big the dropout is.
The smaller the resistance, the higher the dropout, the higher the resulting memory voltage.
What we are going to do now is solder a trimmer to Pin 9 so we create a second dropout which we can manually control. Connect one pin of the variable resistor to Pin 9 and the other pin to Ground (Pin 11 works good, but any ground is fine).
I found a variable resistor of 500 Ohm works best. At 500 Ohm it will increase the memory voltage by 0.25V, this takes the BIOS setting into account.
Resistor at 500 Ohm: BIOS set to Normal results in 2.85V. BIOS set to High results in 2.95V.
The highest memory voltage you can reach with this mod is 3.05V, at 248 Ohm (BIOS Normal) or 316 Ohm (BIOS High).