I have a 95 Cincinnati arrow 500 with an FNC control that screwed up today. It went for a tool change and while is was approaching the tool it did a free fall and stopped about an inch short of the tool holder with an error code. The code is (9178 z axis excessive following error). So I did a bit of testing. I ran the z axis up and down at different feed rates. It is fine until it hits 90 IPM in the down stroke. At 90 IPM it makes a loud vibrating sound, but still moves without the error. At 100 IPM it will free fall and stop with the z axis excessive following error. It will travel upwards at any speed with no noise or errors. What should I look for next?