[wmgeorge]

https://en.wikipedia.org/wiki/Variable-frequency_drive FYI A equipment ground has nothing to do with VFD missing a phase. Nor does not using Shielded cable. Zener Diodes are used for voltage regulation, IGBT are output transistors used on VFDs, welders and many more. If you need to spin start the spindle, sounds like a phase is missing. Simple things first, check power wiring from VFD connections to motor wire could be loose or broken.

[justCNCit]

I may buy one of these cheap replacement units:

https://www.ebay.ca/itm/2-2KW-3HP-VF...torefresh=true

I've checked the power wire from the VFD to the motor and its fine.