There is no configuration setting for the knob range or offset, as the analogue scaling circuit has been quite reliable. The analogue circuit uses the -12V supply as a reference to offset the knob value, which is scaled, inverted, and summed with the CV input. (In hindsight, it would have been better to use a negative precision voltage reference, but this is the design decision we took at the time.)
What this means, is that if your power supply outputs e.g. -12.1V instead of -12v exactly, you might get too much of an offset and the knob won't reach the full ADC range. This would be quite unusual.
Do you have access to a voltmeter to check the output voltage of your PSU?
