wiring encoder/drive shield wires to control GND bus

[unsaint32]

At my work, we have Controllogix 1756 L71 with DI, DO, and a servo card (1756-MO2AE). Today, a DI terminal was occasionally not registering input signal. We also noticed that the servo card was not working. My boss concluded that the shield wire grounding on the servo card was the problem. He told me to disconnect all shield wires from the servo card chassis terminals, twist them together and land them on the GND bus that was used for general control voltage.

As you can see in the picture I am posting (it came from the module manual), there are two terminals in each channel for landing shield wires to chassis: #11 for drive wire shield to chassis, #23 for encoder wire shield to chassis.

I don't know what the optional k-module is, but we don't have that.

Q1) Could the the wiring had been switched by accident? (the encoder wire shield to #11 instead of #23. However, even if so, could that possibly cause that big of a problem?

Q2) What kind of problems could happen, now I wired the encoder and drive shield wires to the control GND bus?

Q3) Does anyone know if this servo card has some kind of fuse I can reset?

Thanks.

 

[Ken Roach]

I think those shield terminals are connected together internally; the reason they are separate is just to give you two screw terminals for the two shielded cables that are typically connected per channel.

That wiring diagram is from a specific application manual associated with a TR Electronics encoder that sends absolute position data via a pulse burst. The K-module was a buffer, I think. That's not the general-purpose wiring diagram for the 1756-M02AE.

I would check the voltage of the DC power supplies, relative to chassis ground, and check to be sure the terminations are secure.

A floating DC common wire would explain both the motion module and input module failure to detect input signals. Unless there is a red OK light, I don't think the module is damaged or faulted.

 

[unsaint32]

Thanks Ken. i will check for power supply and floating com screws. Will update. thanks.