necro for psa purposes…
My Huanyang Chinese spindle was not grounded, despite earth being connected to the ground pin. The pin has no internal connection apparently. I read on other forums this is common with these things.
So for safety when using these spindles, you should measure ohms between the ground pin and the metal case of the spindle with a multimeter. If it is open loop (likely), you should modify it accordingly.
This can be done by disassembling the top, adding a screw terminal inside and soldering a wire to the 4pin connector (difficult).
Alternatively, just remove one of the top bolts and sand a spot above the hole to bare metal. Then connect an earth wire to a loop terminal, and tighten it on the bare metal with the original bolt. Verify continuity with a meter before use.
Most of the Chinese vfds also don’t have a second ground terminal to match. Stacking spade terminals is an easy way to use one earth screw terminal for the mains and the spindle.