machine setup

I have a home built cnc router table that runs in one direction just fine and makes noise and skips steps on the reverse direction (all 3 axis). The computer is an older P4 with on board video and parallel port with Debian Wheezy and Linuxcnc 2.7.0.

I have tried 4 different motherboards and 3 different power supplies and still the same problem. I have used an external power supply for the C10S breakout board and the computer power and still the same problem.

When I connect the parallel cable to my laptop the problem goes away.

So my question is what could cause the machine to run in one direction just fine but not the reverse and what is different when the laptop is connected?

My best guess would be week 3.3v parallel ports on the boards that are giving you trouble. Some parallel ports have true 5v outputs, and some don't. If that is the problem adding an inexpensive parallel port breakout board (such as a C10) that boosts the 3v signal up to 5v should fix the problem.

the c10s and c10 boards are the same boards with the exception of the connectors for the wires.
do you think a pci parallel port card could fix the problem?

A new update. I had an idea to try and run the stepconf wizard and set up a new machine configuration and everything works just fine, all axis run in both directions without conflict so I am guessing at this point there is a conflict in the configuration files.

Now, were to find the conflict?

Timing was to short, most probably.

How do I check the timing?