Stepper motor configuration

Machine: _K90

Board: _Cohesion 3D control board

Firmware: _Smoothie

I have a motorised Z table, but I am having problems with the stepper motor drive, it partly works but the motor seems to be “jumping” and missing steps (buzzing sound but not rotating) I have increased the current in the config file from 0.8 to 1.2 but it made little difference. The moter is rated at 1.5 amps per phase, is it safe to raise the current settting above 1.2 or am I in danger of damaging the control board? (the motor will only be moving for a few seconds on each job)
I have tried to reduce the belt tension to reduce the load on the motor but then I get the problem of the belt slipping!
Any ideas??

Might check wiring to make sure they are not crossed.

What Z table ?

Be sure of the step/mm.
Try a low speed, 1 or 1.5mm/s or 100mm/mn.