Retrofitting a 3-axis VMC with DC servos - guidance needed

Japoo_Ness wrote:

From what I've measured, the issue seems to be on the encoder side.

Shielded cable, shielding grounded on the Mesa side.

Japoo_Ness wrote:

According to the diagrams, the analog signal for the axis is connected to the machine's frame/ground.

Analog cable has 2 wires plus shielding, shield must be grounded on the Mesa side, and one of those 2 wires is the analog ground.

Japoo_Ness wrote:

Is it better to isolate the analog ground from the system ground? Under what conditions is it strictly necessary to tie both grounds together?

There is no exact reference for it, see above, use a DVM to measure between analog and machine ground both in AC and DC mode > if any of those read more than a Volt or two = do not connect. If that is all correct but still does not work, you can try grounding the analog ground to machine ground through a 1K resistor for a single line, test with only a single line/analog drive/connection to mesa.
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As a general rule, use a very good power supply for the Mesa as the encoders are powered from it.