Z axis won't move below a certain point

HI everybody.
I'm facing a weird issue while using with my prusa i3 since I've decided to pass from the sprinter to the marlin firmware.
My Z-axis don't want to go to home position and when I move it manually it won't move below a certain points.
I have checked my end-stops and they works fine (M119 command work fine too). I don't think that it's related to them cause I've try to triggered them and ask my Z-axis to go to his home position but it doesn't change anything.

It's really weird because if I ask my Z-axis to step up and to go down after that, it will work. It's only stop going to below a certain point on the Z-axis and it's always the same. He act like he reaches the end-stops but it doesn't...

I've also try to slow down the HOMING_FEEDRATE option but I'm not sure about what I did
I've changed this original line : #define HOMING_FEEDRATE {50*60, 50*60, 4*60, 0}
to this one. #define HOMING_FEEDRATE {50*60, 50*60, 4*10, 0}

There is some informations about my printer:
Prusa i3
Marlin firmware
Only mechanical end-stops (NC not NO) in MIN (only 3)
Linked below is my configuration.h

Any idea of a solution ?
Thank you very much

If it were my Delta I would suspect your z_max_pos is set wrong (too small) and you are hitting the software endstops (z=0) before you actually reach the bed.

If it stops at the same point, measure the distance to the bed and try adding that to z_max_pos. Then carefully lower z to confirm. If you are truly daring you can set z max higher than it's supposed to be and then jog down until it grabs a piece of paper. That distance you jogged down is the real z height.

Keep in mind I've only messed with Deltas.

Marlin can be tricky sometimes with the first installation and setup.
Also keep in mind Marlin does the coordinates from the Home position, that means when you turn your machine on with the 3 axis not in Home they can only move away from Home but not towards it.
This "bug" can be used to confirm the stepper directions and negations.
If you can home properly move in 10mm steps till you reach the point of failure, then try again but for the last bit do 1mm steps till you reach the end.
The number you get should be pretty close to any software limit that might be set in the config.
So check if the config actually matches your physical dimensions.
Messing with the Z-offset won't help, it is more to adjust for different materials or bed heights without messing with the endstops (or to continue a faulty print).

Thank you very much guys, I don't know which of your two solutions solve the problem because I have tested them at the time but now it's working like a charm.

If you have the same problem, here is some good link to look to:
1- Command M500, M501 & M502
2- G92 X0 Y0 Z0
3- M360: Report firmware configuration
4- #define Z_MAX_POS 200

Edited 1 time(s). Last edit at 01/28/2016 06:48PM by tlahitte.