Model of the VFD is an HY02d223b I think, picking from the options in the manual. Running a 24K 2.2kw spindle, air cooled.

I am running a uc100 controller (via UCCNC) with a c35 BOB and a C41rev3 PWM board from cnc4pc.
After dropping the project for a number of years, a router rebuild of an ancient camtech (1995!), my big machine's spindle died and I have some time on my hands and have promised to sell this older machine to an ex-employee but hadn't gotten it to 100%

I am currently trying to control the motor speed.

After reading and taking Mactec54's advice of using a relay for the motor control and deciphering cnc4pc's barely implied hints in the c41 manual, I have the on / off working. Speed control, not so much.

UCCNC is set at min speed .001 and max speed at 24K rpm. PWM Hz at 300 and 0-100% range.

I have tried most everything I can think of and have confirmed that UCCNC is using the correct pin for the PWM and the output of the C41 does seem to work as I have the proper voltages across the ACM (multimeter's -) and VI (multimeter +) connections on the VFD.

The VFD has been reset and parameters confirmed as per the big huanyang thread but that changed nothing.
I'm using min speed as 200hz / 12000 RPM and max at full 400 hz / 24000rpm due to the air cooled spindle.

If I set the VFD to external control on PD002=1 (and PD070 at 0 for 0-10v) I get only the minimum 12K RPM and changes in the VI voltage do nothing.
If I set the VFD to PD070=1 and PD001=0, then I have the full range of 12K-24K RPM from the onboard pot
If I set the VFD to PD071=0 I have an odd range of 12K to 18K rpm from the onboard pot

(I suspect that is because PD073 is set to 200 and PD072 is set to 400 and the 5V the onboard pot is putting out is in the middle of that new range......I have seen Mactec54 recommend PD073 set to the same speed as minimum hz but that doesn't put 0v at 0rpm as one might expect.....it works if you have the same settings in UCCNC though.)

I'm at a loss of what I am getting wrong here but I'm done for the night trying to figure it out.

Other settings are per Mactec54's posts and I have tried both PD044 at values 1 and 2.