Please help - missing steps ... Mach3

[JAZZCNC]

What voltage do you have coimng out of the PP.? This problem sounds very much like PP is low power probably 3V type. This will cause the problem you are having because there isn't enough voltage difference between HIGH/LOW.

Also one more thing that can cause this and in some way related to the above is if your Step pulse is on the wrong edge of the pulse. ie: On the down slope(falling edge) when the controller is pulsing on the up slope (rising edge). This affectively puts the timing out and you'll loose one step with every direction change.
To test this for each Axis just write some G-code which moves the axis Back n forth small amounts but 1000's of times very fast.
ie:
G0 x10
x0
x10
x0

Copy and paste into a file to make several 100 lines. Make a Mark before starting and run the file. It should return and if it doesn't then you are on the wrong edge of the pulse.

Some drives will let you select the rising or falling edge, Some won't. To Force or change the edge just toggle the Active Low in Motor outputs. This will reverse the motor direction. So goto Homing and Limits and Click Reversed for that axis.

Try and let us know.?

Or better still do your self and machine a favor Dump the PP and get your self a external motion controller.!! . . . You won't regret it.