When I try to jog my spindle up and down with the page up and page down keys on the keyboard it is random as to which direction it actually goes, sometimes when I press up it will go down then I press up again and it will go up, then I will press down and it will go up and then next time down, just always random. I still moves perfectly in the x and y directions. This just started happening a couple day ago, wondering if anyone could help. If I try to cut something it still goes in random directions only in the Z. I have had this machine for 4 years so it has worked very well before. Please help. Possibly a short somewhere in the system?

P.S.    I'm using Mach 3

I will try to re install Mach3 and have a new .xml file created which you should customize to your settings. Also I will check the Z axis motor wiring

That seems like a last resort option, thank you so much for posting. Any other advice?

Perhaps thoroughly check your wiring and all connections - vibration or movement could have caused a bad connection.

Tweakie.

I agree with Tweakie, I had a very similar problem a few months ago, it turned out to be a loose wire in the stepper motor connector, once fixed it works great

Nick

Yes you guys were right, the parallel port wire had come loose at mother board. Thanks for all the help!!!