Intermittent Z Axis Spike with Yaskawa Servos, 5i25/6i25 and 7i77

So another analog channel worked but channel 4 always fails eventually?

Correct. Analog output 4 fails after anywhere from a few minutes to an hour or so. I've had the machine up and idle with Z on analog output 5 for over 8 hours now with no spikes.

In that case its probably best to get an RMA and return the 7I77 for evaluation/repair/replacement

I sent you an email as a follow-up. we can take the rest of this conversation offline.