The display does not light up? Check cables and power going to the Calmotion board. Also note that the gray display cable should not be more than 7 feet long.
The Calmotion operates but fails with the communication:
The most common cause is that the parameters on the Calmotion unit got changed accidentally. Or the CNC controls parameters where changed.
If the parameters of the machine and Calmotion where originally written down somewhere, check that first.
Check the cables have not disconnected.
No response at all?
Check the baud rates, the CNC and Calmotion baud rate must match.
Check setting "START Rx" typically this should be set to "Automatic"
A short program loads but a longer program fails to load into CNC?
Check the Data Bit/Parity/Stop bits (Majority of CNCs use "7, Even, 2")
Check the Flow control. (Majority of CNCs use "SW XON/XOFF" which is another term for DC codes).
If the programs sending to CNC have a % at the start and the end, then set the Calmotion START Tx and END Tx parameters to "none"
With external units, possibly the RS232 signals were damaged. With a DC volt meter, check for approximately +/-8 VDC between pins 7-3 and pins 7-5 on the Calmotion DB25. The pin #s are imprinted in the plastic next to each pin.