Yes you can

I will start with a warning. It is unknown if this is safe. KnC may have turned off the VRMs due to that there is a problem with the design.
You board might burn! On the other hand they ran with all VRMs turned on for a few weeks when they were new without any major issues.
I have run a few machines with 8VRMs for almost 2 weeks without problems. Some machines will start buzzing pretty loud, I have no idea why.

Suggested procedure to enable all 8 VRMs:

1. Change all voltage adjustment to at least -0.517.
When all VRMs are turned on the adjustment will be from a base of ~0.9V,
-0.517 will give a voltage of ~0.85V which works fine for 1Ghz.
It may work fine with lower values, such as -1.0V at lower clocks. I have not experimented much.
With -0.5V and 1Ghz the machine will pull over 900W from the PSU (~220W reported per board).

2. Stop cgminer/bfgminer
Run on a shell:
/etc/init.d/cgminer.sh stop

3. Run the enable.sh script. (see below)
The script will take the voltage adjustments of the "official" 4 VRMs on each board and make sure that both VRMs for each die will have the same adjustment. It also turns on all VRMs.

4. reboot. Do not power cycle.
The VRMs have a tendency to get upset when they are turned on the first time and set error flags and in some cases not start properly. A reboot cleans things up.

5. Verify on the advanced settings page that the current on each pair of VRMs is in the same ballpark. The pairs are 0+1, 2+3, 4+5 and 6+7.

6. Overclock as usual

Each time you apply a voltage adjustment in the advanced page you have to run enable.sh again to make sure the pairs have the same adjustment.
This is VERY important!.


The script is safe to run on a machine with mixed 4 and 8 VRM boards. You may get some error message when the script tries to tank to the missing VRMs.

If you powercycle the machine I am pretty sure all changes are gone. I haven't powercyled my machines since October when there was a storm and we lost power for a few minutes.


The script (enable.sh):


#!/bin/sh

# Fetches the TRIM settings of the official 4 VRMs and sets the
# same value into each paired VRM.
for b in 3 4 5 6 7 8 ; do
    v0=`i2cget -y $b 0x10 0x22 w 2>/dev/null`
    if [ "$v0" != "" ] ; then
        i2cset -y $b 0x11 0x22 $v0 w 2>/dev/null
    fi

    v1=`i2cget -y $b 0x12 0x22 w 2>/dev/null`
    if [ "$v1" != "" ] ; then
        i2cset -y $b 0x13 0x22 $v1 w 2>/dev/null
    fi

    v2=`i2cget -y $b 0x14 0x22 w 2>/dev/null`
    if [ "$v2" != "" ] ; then
        i2cset -y $b 0x15 0x22 $v2 w 2>/dev/null
    fi

    v3=`i2cget -y $b 0x17 0x22 w 2>/dev/null`
    if [ "$v3" != "" ] ; then
        i2cset -y $b 0x16 0x22 $v3 w 2>/dev/null
    fi
done

# Turn On all VRMs using "on" in OPERATION
for b in 3 4 5 6 7 8 ; do
        for d in 0 1 2 3 4 5 6 7 ; do
                i2cset -y $b 0x1$d 1 0x80 >/dev/null 2>&1
        done
done


What the script does is that it reads the voltage adjustment register (VOUT_TRIM, address 0x22) from the official VRMs (0x10, 0x12, 0x14 and 0x17) and writes the same value to the other VRM in each pair. And then it sets the "On" bit (0x80) in the OPERATION register, address 1.