What is the nature of the problem? does the M3 work ok? As you probabally already know the M4 usually just output the spindle reverse signal and the FIN signal will wait until the up-to-speed, before the program will continue, it is usually very little ladder.
The Fanuc software and programmer cost a bundle unless you can rent of off someone. If it's an original bug, what about recourse back to the machine tool builder to correct it?
Is the Fanuc set to display the ladder on the screen, with bit status?
Al
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.