Yes turn it anti-clockwise.. make sure it doesnt go past the 6pm mark or 12 pm depending which way you hold it.. As i think that will increase it again.
You will have to decrease your clock rate too or you will get hardware errors with the lower voltage.
I set a clock speed like 150 and with it mining slowly turned the screw anticlockwise.. Noticing when the HW errors started then turned it back up slightly.. It will give you a ball park area that way.
