How to debug a hardware problem?

[cenglish]

Last weekend I put limit switches on my X2 clone. While I was at it, I replaced all the stepper motor wiring with shielded cable and put db9 connectors on the cables about 8" from the controller so I can disconnect the controller from the machine when I need to pull the mill out of its cabinet. After I got it all back together, Mach3 shows the DRO's moving but I get no movement on any of the axes. I’m looking for advice on how to troubleshoot the problem.

My controller consists of:
•        (3) SideStep Bi-Polar Stepper Motor Driver
•        PBX-2 Parallel Port Breakout Board
•        24Volt 6.5Amp Switching Power Supply

This controls (3) HT23-260-4 Stepper Motors.

I get red led lights on the breakout board and the driver boards. While I haven’t done it yet, I’m going to do a continuity check on the parallel cable between the PC and the controller. I did disconnect the db9 going to the limit switches to see if that was causing the problem, but the problem continued so that’s not it.

What should I check next and how? Obviously, I need to check the cable between each driver and the female db9, but if it were a cable issue, only that motor would not turn. I’m all ears if you have a suggestion on how to troubleshoot this issue.

[Hood]

If it was previously working and you have not changed any settings in Mach apart from setting up limits then it would suggest that you have a wiring issue.
 Starting at the computer and working out is the best way especially as it is all axis that are the issue so you are on the right tracks by checking the PP cable first. If you have a volt meter you can test the direction pins to Gnd pin whilst jogging each axis back and forth, the voltage should change between 5v and 0v as you do so. You can also check between step pins and Gnd but depending on the active state you will either see a small increase in voltage or a small drop, so it may be 5v at rest and maybe 4.8v jogging or 0v at rest and something like 200mv jogging.
Hood

[cenglish]

Hood,
Thanks for the advice. After spending hours rewiring the mill I was in a hurry to test it before dinner. I had failed to connect the PP cable! That's the good news. The bad news is that one of my solder joints in a db9 connector was bad and I ended up toasting my Y-axis stepper driver:( Live and learn. I've ordered a new one and decided to replace my breakout board with an isolated one from Probotix while I'm at it.