My VFD which looks like yours Huanyang had exactly the same problem would work only in th morning and at night when it was cooler and after 5 - 10 min would have an error. I bought a dirt cheap VFD called NF9000 on ebay wrote the linuxcnc drivers myself
forum.linuxcnc.org/30-cnc-machines/34340...vers-for-nf-9000-vfd
