The problem is that #4 drive does not move but it has power. The motor does move in the test mode
As Steve asked: is this "test mode" the PMDX-126's built-in test mode? If the PMDX-126 test mode is able to move the motor, then it is most likely a Mach3 configuration issue (still), SmoothStepper or ribbon cable (SS to PMDX-126) issue.
and when I plug into another driver it will move.
I'm not sure what you mean. Do you mean when you plug another Gecko driver into the 4th position on the PMDX-134? Or do you mean that when you unplug the motor from the 4th position and plug it into the 1st, 2nd or 3rd position the motor turns?
Have you tried swapping Gecko drivers? For example, swap the gecko drivers between the 3rd and 4th positions. Does the problem stay in the 4th position? Or does it move to the 3rd position?
You can also use the LEDs on the PMDX-126 to help diagnose things. PMDX-126 connector J1 has screw terminals and LEDs for the parallel port pins 8 & 9. You may not be able to see the step pulses on the pin 9 LED, but you can see the direction signal. Jog the A axis one direction and see if the "Pin 8" LED is on or off. Then jog the other direction and check the "Pin 8" LED. If should have changed from "on" to "off", or from "off" to "on". If that works, then go into Config->Ports & Pins and assign the A axis direction to pin 9 (temporarily), and step to pin 8. Re-run the above test looking at the "Pin 9" LED. It should change when you change jog directions. Restore the A config to step on pin 9 and direction on pin 8.
Bob