x axis only moves one way

I have a weihong DW1325 router, working ok for last year, now jogging or running program any X plus or minus command moves minus. have swapped stepper motor and driver, these are not the problem. So i guess it must be the NC Studio 3D card, or the Fuling DZB200 inverter or the vfd. Can anyone tell me how to narrow down the issue, dont want to replace lots and find still have the problem, also this happens about half the time, so ruins every job. cheers, Doug

Problem solved
Changed 3D card (NC Studio), appears to be the correct guess, and the least expensive, Cheers, Doug;)