MESA 7i76E burning out issue

A while ago, my MESA 7i76E broke; one channel just stopped working. I wrote about that here . I then found someone who repaired the card, after which the machine ran fine for half a year. He said he "replaced the resistor network" of the channel.

Today, the exact same issue appeared again. Joint 2 stopped working and after a restart it worked for a minute and went away again. This is exactly the behavior I saw last time.

This time though I was better prepared and had a spare 7i76E ready to replace the other one. After replacing it the machine ran fine - but after an hour the new card displays the same behavior, too! Clearly something is going on that breaks this channel... sometimes.

What would you do to diagnose this? Replace the JMC servo (with the built in controller) and hope for the best?

If Step/Dir resistor networks or driver chips are being damaged
it means a voltage considerably outside the 0 to 5V range is being
applied to the Step/Dir pins.

First thing I would check is drive grounding and Step/Dir wiring
Routing step/dir lines parallel to servo motor wiring might also
cause enough EMI to damage the drivers.

An intermittent short to 24V wiring is another possibility.

Thank you, that makes it more clear. I will measure all the cabling and ground connections.

Nope, 3 axis 4 joint CNC. I doubt EMI could be it, that data cable is shielded, less than a meter long and separate from power, too. But I'll check every wire.