-the power supply /12VDC typically min 300ma/ for the spindle 0-10v, must be separate , do not just take that voltage from somewhere else

-change the trimmer on the output of the board, the one that regulates the 0-10v, or even upgrade it with proper potenciometer

-no need for additional caps if all is working fine. reset back VFD to what it was originally and first do what i suggest above


At the end of the day a crappy BOB does that, i have seen it. So change BOB, or add additional spindle speed controller board /30-40$/

Ahhh, and dont run the spindle at 24k rpm. Or you will shorten its life considerably. In fact never run it more than 18k rpm. And then first run it for a couple of hours at slow speed so grease and bearing sets.