Relay boards repair, troubleshooting, and CNC realy board information

Relay boards are very common in CNC machine tools. They come in many designs and shapes. The one thing relay boards have in common is that they all function the same, so learning how realy boards is simple. Basically each relay converts an I/O signal which is typically 24vdc or lower into a signal that is typically 24VDC or 110VAC. The reason for converting this signal is due to high loads or amperage causes by pulling in solenoids contactors and other devices. By using relays the control can fully isolate and use alternate power supplies with fusing instead of shorting out the power used to run the inputs and outputs from the I/O.

Below is an example of a relay board. Notice the individual relays mounted to the circuit board. Also notice the Red 100VAC wires out the bottom and the gray honda connectors on top which the Output signals from the I/O attach.

Troubleshooting relay boards in typical CNC machine tool applications Again notice the LED's on the relay boards. Many service people do not understand how they actually work. When the machine commands an output. Each output turns on the LED. The power from the output cards of the ladder turn on the LEDS. When a relay board LED turns on it means one thing and one thing only which is that the output has made it to the board and should be applied to the relay mounted on the board. The power pulls in a coil on the relay. The coil closes the contact closes and then outputs 110VAC or some other voltage through the contact and sends it to a load (contactor/ solenoid etc.). If the circuit is not fused and a coil burns out it will burn up the contacts in the relay and not damage the I/O.
Relay board repair Relay boards can be repaired usually fairly easy. Many times traces get burt up on them. Typically you can just solder a new wire where the trace use to be. When a relay burns up you can unsolder it and put a new one in its place. Many times there are also circuits/relays not being used on the last relay board. They can often be used as spares.

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