Prusa i3 z-axis slipping

I recently purchased this printer:

[www.amazon.com]

As my first venture into 3D printing. I'm having a problem, and was hoping someone here could help since i'm having a hard time getting support from the company I purchased from. It is a version of the Prusa I3 and has a MKS base 1.2 control board.

The left motor controlling the Z axis seems like it is slipping, almost like the motor is not strong enough. It only makes it about 1/2 sown the screw drive before slipping. Is there a way to adjust the torque on these motors, maybe by way of more voltage?

If so, could someone walk me through how to do this?

Thanks!

Decrease your max feed rate for the z-axis in your firmware.

Thanks for the advice. I saw a similar solution in another thread, and I changed the setting on the LCD screen from 5 down to 3, though it didn't seem to help. Would this be the same as doing it in the firmware? If not, how would I need to do it?

You need to make sure your X axis moves freely up and down and not in a bind. The Z axis guide rods should rotate freely with your fingers for the z axis travel range. If not spread or compress the assembly end pieces . If the assembly is not free to move but in a bind the steppers may not have enough torque to overcome the misalignment.

Everything feels okay when moving by hand. One side was a little tight at first, until I made a few adjustments. I can actually get the axis to move up and down now, but both sides still "slip" once in a while. Could the motors have been weakened from binding before?
The ends of the X axis are 3D printed and slip onto the X axis bars. I've adjusted the ends in/out to try to get the Z axis poles perfectly straight, but it seems like there is no magic spot to make this work. Too far in, and the motors bind when the axis is at the top. Too far out, the motors bind when the axis is on the bottom. Sometimes, the axis goes all the way down, but slips when going back up.

My printer might be the same as yours. I can't run mine because the brass flange nuts were not correct for the threaded Z rods. Waiting for them. You might check how well the flange nuts rotate freely and maybe some light oil.

What kind of oil would you use?

I would use a light oil that is used in air tools. This oil is common in most hardware stores. It is a liquid. Some of the spray on oils become gummy and I would avoid them. Have you tried the nuts individually to see if they moved up and down the rod freely? If they do not and have tight spots that can be fixed.

I put a little machine oil on the rods this morning and that seemed to help. Trying my first print now- we'll see how it goes!