Prusa calibration issues

Hi everyone, I’m having some issues calibrating my prusa i3 mk2 - anyone able to offer some pointers? My initial look at the web hasn’t found any similar issues (or I’m being spectacularly daft and missing something blatant).
Basically it passes the selftest but attempting to calibrate xyz crashes the print head into the bed over the first calibration point - i.e. following prusa’s flow passes stage one but not two. The probe works (both on selftest and in terms of holding an object up to it and confirming the telltale light goes out), and it seems to detect the points when i move it manually. Setting the probe lower does not seem to alleviate the issue, which is weird.

Small amounts of kudos/chocolate to any winning answers - I’m probably going to bring it down to the space to have a tinker with next week if nobody has any ideas.

(@lewiss ?)

Try lowering the probe height - ie make sure the bottom of the probe is level with tip of extruder.

One of the things I’ve tried - what happened was the probe hit the bed instead. I’m playing about with the height but no matter what I do I have the same issue.

I see P.I.N.D.A. probe goes into connector Z-Min and signal ends up on Atmega2560 pin 23 (schematic sheet 2/5). I suggest test pin goes high when probe is engaged.

What software have you got on there?

Is It run on an Arduino ramps board with Marlin?

Possibly the bed height is set wrong in configuration.h file

@dsikar thanks for that - I will look at the pin in question and see if all is running correctly.

@lewiss It’s prusa’s native board - “rambo”. I flashed the latest firmware (Feb 17 I believe) and the issue persisted…
I’ll sit down one evening this week and have another crack at it. I’m probably missing something, I just wish i knew what it was!

Well for closure, the thing which was wrong was I had assembled the mounts for the top of the z rods upside down.
I did say I was probably missing something…