Z-axis stepper judder

Just completed the hardware, electronics and wiring of a Prusa Mendel.

Downloaded the Arduino environment, plugged in the USB and comms are up first time. Downloaded TestCode.pde which shuffles the X,Y,Z,E steppers back and forth as well as make the LEDs on the RAMPS board flash.

Started with the fully counter-clockwise of the Pololu current limiter pots then up 25%. X,Y and E all moved back and forth!

However, Z just vibrated. So turned up the current limiter and the juddering got louder (more violent juddering). Turned it all the way down and it stopped.

I've swapped cables around, Pololu boards into different slots, disconnected one of the Z-axis stepper motors. I've swapped Pololu boards, cables, stepper motors and in any combination, all Pololu boards, cables and motors work as long as they are NOT using the Z-axis socket on the RAMPS board.

If I use the Z-axis socket to drive any of the other working stepper motors they stutter.

So, is it possible I've cooked the RAMPS board but not the Pololu?

Is it something in the Arduino end or the TestCode.pde file?

As a RepRap newbie I've got no real idea where else to look. Any suggestions gratefully accepted!

Regards, Mark H.

Check for open/short circuits around the Z driver socket, especially the DIR pin and output (1A-2B ) pins (schematics).

Thank you! Thank you! Thank you!

Rebecca, you're a star. I assumed that since the RAMPS board had arrived ready-assembled that it had been tested and was ready to go. However, after high-powered magnifying glass inspection, I noted several minor shorts and some pads that weren't connected to anything: all around the Z axis socket. I cut the shorts and bridged the gaps and tentatively turned the psu back on. Immediately I could see that ALL the axes were working.

I have to add the heated PCB and I'll be ready to rock'n'roll. Thanks again.

Regards Mark