I must say that I don't understand how this is working! The hddb2 board has a constant 12V on the 12V output pins, not controlled by UCCNC. There should not be a problem with the output pins - they do not deliver any power, they are open-drain Mosfet outputs. In effect, an electronic switch with one side connected to ground. The manual shows that these digital output are completely independent of the analogue signals. That's why the VFD is configured to use its internal 24V supply so that you control it by switching the DI inputs to ground. I would not be happy to use this setup as it is now wired because I do not understand how it works at all!