I have inspected what the November firmware has actually changed.

What I can see it has changed a value in one of the registers in the VRMs. It has set the "ON" bit in the OPERATIONS register,changing what conditions are needed to turn the VRMs on.
This change will be permanent even if rebooted or power-cycled. It can be changed using i2c commands:


Turn all VRMs on:

#!/bin/sh
# Stop SPI poller
i2cset -y 2 0x71 2 0

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


Restore to factory settings:

#!/bin/sh
# Stop SPI poller
i2cset -y 2 0x71 2 0

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 0x0 >/dev/null 2>&1
        done
done


I suggest stopping cgminer before doing this to limit the power when the operation is done.

Reading the datasheet for the VRMs I can see that when using them in pairs (as we do when all are turned on) there are some requirements on how they should be turned on. This method does not do that!

I have heard that hizzing sound as well. Some boards do that. They did that on 0.90 firmware too. No idea why.

I do not know if this is safe or not, it might be unsafe and burn your boards.