False outputs

Hi everyone. I am working with a ABB 1400 M98 and controlling two servo motors for positioning weld fixtures. Each servo has 4 positions 90 degrees apart. These are commanded by using outputs from the robot’s controller to the servo drive. One output for each position on each servo so 8 outputs in total. Once yesterday and once the day before, the servo rotated without any command. Once on each servo and a different position on each. However, on the teach pendant i/o screen, none of these outputs were on. Has anyone had a similar problem? Is there any way that the i/o board(328 i believe) could malfunction and quickly send a signal out? As far as I can tell its not a wiring issue. Thanks.

I have not heard of outputs malfunctioning and going high randomly (only not working at all).

This being a welding cell using a shielded control cable, ensuring the shield is correctly earthed , and if possible running the control cable away from any welding cables (power or earth return) would be the place to start.

Often induced noise in control cables causes issues.