weird z-homing problem. Been stuck for days... [SOLVED]

Hi all!

I'm building myself a custom Reprappro Mendel, but are having troubles getting z home to work.

When I send G28 Z (home z axis) the z-axis moves ca 1 cm in the wrong direction at the fast home feedrate speed. It behaves as if I sent it G1 Z10, just slower. No bounce back. Tested with different versions of Marlin, same result.

Sending M119 gives me "z_min:H" no matter how what I do with the endstop swich terminals (like shorting, unplugging or trying different swich). I've looked for shorts on the Melzi board without any luck. X and Y homing works as expected...

Configuration.h

Any suggestions?

Edited 1 time(s). Last edit at 08/22/2013 06:37PM by tobben.

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torbjornludvigsen.com

Measured pin 20 on the atmega 1284p. It jumps between 0 V and 5 V when endstop swich is pressed, exactly as it is supposed to. pins.h contains

#define Z_MIN_PIN          20

just as it should do. Where to look for errors now?

I only get the correct jumping between 0 V and 5 V if I measure in the "measurment hole" beside the processor. It turns out that if I measure directly on the pin solder, it gives a constant 5 V. Carefully measuring resistances between holes and pins with power unplugged shows a bad soldering job on pin 20. Oh my, hope I am able to fix it, and hope it's the only one...

Guys, I made it. The machine works now. Lession learned: If your pin 20 on your atmel 1284p is not connected to your Melzi PCB, the consequence is that z-home jogs ca 1 cm upwards instead of heading down towards the swich (well, at least if you try to use Marlin).

Thanks for rubberducking me, hope this helps someone