Amplifier Fault on Axis
This occurs at power on if the control does not detect an axis that should be
operational. This is often seen when the A axis is not in use and the dummy
termination plug has been installed. If the dummy termination plug is installed,
this message can be disregarded.
If this message appears for any of the other axes (X, Y, or Z), then power off to check the motor overload relays. Power on and if the message appears again, call the service department, noting the error message number.
Power off the machine before checking fuses, relays, and circuit breakers. The motor overload relays can be recognized by their white reset buttons. They are located in both control enclosures. The white button must be pressed to reset a relay.
This message also appears when the EMERGENCY STOP button has been
pressed. The operator must release the EMERGENCY STOP button and press
the JOG button to reset the amplifiers. (Pressing in the EMERGENCY STOP
button disconnects the axis amplifiers. This is why this message appears when the button is pressed.)

[ 18 ] AMPLIFIER FAULT LINE DOWN
This error appears any time the axis card no longer detects the fault line signal from the amplifier, or the signal strength has dropped below 10V, at least 5V indicating a possible amplifier fault.

bala955, download this manual if you don't have one.
http://www.compumachine.com/Support/...leshooting.pdf