linuxcnc probotix and THCsd

Afternoon everyone,

I am new to this, I was given some parts and have built a cnc plasma table. Started out with some Probotix cards and stepper motors. And a computer with emc2 in it. I got it all running with considerable help from the friend that gave me the parts. He bought other stuff and is building a cnc router, also Linux.

My problem is the Proma SD THC that I have. It runs when it should not and won't when it should.
There is almost nothing written about the SD, lots about the 150.
In my notes I am using the labels on the THC end. So the Dir in actually comes from the breakout board out.
Here is a description of what it does. With no power to the thc the signal should run right through and the table should run as normal. However x and y both work z never moves.
Now power up the thc (12v battery for clean power). The THC blinks and flashes as advertised, the Z axis immediately starts down and will not stop until I unplug the 12v or the driver computer. The Z axis motor is noisy.
I pulled the wires out of the THC and put the Dir in/out together and the Step in/out together. Table runs fine, nice and quiet all three axis.
Leaving step tied through I separated and tested Dir for polarity. I only have an analogue meter. The Dir out has 5 volts positive sitting even whith-out emc being triggered. When I trigger emc to cut then that 5 volts comes and goes, the Z axis operates properly. There was never any negative deflection.
I wired the Dir in/out back together and separated the Step, I got 4.7v ish which drops to 4.3 ish when the z is activated. The z axis did not move when I had the volt meter inline.

Thank you to everyone. In advance.
David

Thank you both! We were discovering that there needs to be a single source of power and very good grounds. Still puttering with it and thinking that the computer does not realize there may have been z axis changes when the cut is finished. Thinking it needs a rezero switch each time from something unmoving like the gantry.

david