Eddie Munster said:

DGG wrote:

At this point, however, I'm beginning to suspect that it may not be a
bad controller per se, but rather improper design/installation which
leaves the unit subject to radiated EMI resulting in CPU confusion.

Is this something you can touch up? (shielding, ferrite beeds) If so you
got nothing to lose, if it doesn't work, put it back how it was.

I'm working towards that very idea. I'm going to monitor/capture any
hash on the lines with a scope to see what is there.

Turning a bowl with a Tektronix scope 2 feet away and wired to the
lathe is probably not particularly good for the scope, however. ;-)

FWIW