X/Y-Axis not move same distance. Problem

Hello there!
I bought a cheap 3D printer on E-bay, CTC I 3 Reprap Prusa. It's a nice construction. It's using GT2560 Rev A. board and Marling, the version I don't now. Everything works nice EXCEPT. I try to print something the Y-Axel don't move the correct distance. I try to print the cube, 25,4 mm X/Y-Axel. The Y-Axel only print about 8 mm, You got a rectangle instead for a cube!

I have the firmware and look to the settings. DEFAULT_AXIS_STEPS_PER_UNIT {78.7402,78.7402,2560,105} // default steps per unit for Ultimaker
Is this correct?

Where should I change the values, if this is the problem, is it here?

Wye should I need to have different number of steps for a given distance between X and Y - Axis when they both have the same belt and motors?

What can I do?

When I move the printer bead from the control panel then everything seems to have right distans.

I use Cura 2.3.1 and have also tried some other software.

I have god tension on belts, everything works smooth.

I can upload new firmware to the board.

Regard

Ola A
Sweden
Linköping

If you have the same motor, same pulleys, and same belts on the X and Y axis, you might just need to adjust the Vref on your Y axis driver.

Were can I find this adjustment for Vref? Is it some hardware issue, perhaps on the stepper motor drive?

Hello there! vere can I find Vref and can someone explain the function for it?

Vref is the voltage reference on your stepper drivers that control the amount of current flowing through your drivers.
On each driver board there is a small silver adjustable regulator. Measure the voltage between ground and the adjustable resistor. They should all be the same.
If the voltage on the problem axis is lower than the others then it may not be getting enough current to the motor.

Google adjust driver current on 3d printer.