Inverter malfunction of lathe

Our lathe have been custom that an inverter installed.
As a result, we are supposed to be able to change the revolutions in the volume steplessly.

Inverter is slump .
I bought in an online auction.Cause it?

Sometimes works normally, sometimes I get an error. I do not really understand.
So replacing the inverter.
This motor is 5 hp. 3.7kw.
I've searched it to  an internet auction again.
3.7kw is not a little popular. Many have not been exhibited.
Moreover it is a little expensive.
Cheap.
The inverter is the price seems to have come going down.
The new one is black. The old one is gray.

Difficult work we've done recently with the lathe are these.
Atsubomb and Tattsuan made these bytes sharpening by hand.

We shaped a ball.

Atsubomb made ​​a collet. We have a lot of quantity do the job.