Circles are Oval after creating my own 3D Printer

Hello,

I?m Alexander from Germany and new in the 3D printing community.
This weekend I finished to create my own 3D printer (similar the HyperCube design).

As basis for the board and power supply I used my old Geeetech Prusa I3 (Wood:rolleyes:). All other parts are new.

After I had a few test prints I saw that the circles which the printer prints are oval instead of circular. During the building I needed to extend one of the stepper motor cables in order to reach the board. Therefore I cut of the connector and soldered a piece of cable (different ?) to the stepper cable.
Could this already be my problem? Should I do this with all steppers in order to get all cables to the same length and with the same different ??

Is there anything else what could happened? I already justified the stepper motor drivers all to exactly 1.0 V.

I hope someone can help.

Thank?s!

is it belt or screw driven ?

It's belt driven. Unfortunately I can post a link to a picture only after 3 posts...

Edit: I can see.. there is some movement in the y axis when I only move the X axis. Is it important that the two belts (XY-Core) have exactly the same length? Could this occure the problem?