Z Axis Test fails
I had some issues with printing PETG. I was getting blobs on 25% fill. I decided to change the .4 nozzle. After putting in the new nozzle I went through a calibration routine. The X & Y pass with no problem but the X axis won't pass. When the test runs it goes up to the top (reading 221) and then goes down and touches the plate. I double checked the assy was pushed all the way up into the extruder assy. I checked the height manually with a piece of paper. When the height is at 1mm I can move the paper but it has pressure on it. When at 0mm I can't move the paper. Not sure if this is correct.
I did a factory reset which didn't help.
One other thing to note is I have had problems with the Z axis in the past. When starting a print the printer will go down to the bed height to clean the nozzle and then when it starts up it would make a loud noise and the z axis would be way off. I contacted Prusa and they told me to loosen the trapezoid screws. This caused the problem occurrence to a minimum (although once in a while it would come back). The problem would usually go away after restarting the print.
The printer was purchased assembled not a kit. I have probably got close to 1500 hours on it.
RE: Z Axis Test fails
I should mention that I ran the Z calibration before the test and it failed also. The load sensor test passed.
RE: Z Axis Test fails
I had a z-axis calibration failure after changing the nozzle and eventually realised that the nozzle tube thingie was not fully inserted. The nozzle was effectively about a millimetre further out from the extruder than intended and that made the total z-axis range a millimetre too short and that made the calibration failure. I found that out when I found that the z-axis calibration succeeded when I ran it with the removable printing sheet removed.
That might not be your issue, as you say that the "assy is pushed all the way up", but it is probably worth a second look. My assy was difficult to insert fully because of poorly printed extruder main plate. That difficulty went away when I replaced the Prusa part with a modified part printed better (out of ABS) in order to alleviate problems with printing soft TPU ( https://www.printables.com/model/599472-modified-nextruder-main-plate).
RE: Z Axis Test fails
Thanks for the suggestion Michael. I'm sure my extruder is all the way up. When I press it up I can hear a hard stop as it hits the top. I thought there might be something blocking it (a pierce of filament) but it feels like it's going all the way up and my extruder looks like the photo that Prusa posted. I also don't have any way to print another part at the moment since I've only got one printer, the MK4. I've had so many issues with the Z axis I'm considering just sending the printer under warranty back to Prusa if they can't give me a solution.
RE: Z Axis Test fails
@dtice
would be great to know, which FW version do you use.
RE: Z Axis Test fails
I'm using the latest 5.1.2. I've narrowed the problem down to the z axis hardware. I loosened the Trapezoid screws again and it started to work. I'm pretty sure to completely eliminate this issue I'm going to have to disassemble the x-z and check screws and lube the bearings. It's working now so I think I'll do it when I have more time. Unfortunately I didn't build mine (Factory Assembled) so I'll have to watch some YouTube and study manuals before I tear it apart.
RE: Z Axis Test fails
After talking with Prusa I decided to take the Z-Axis apart and recheck everything. I disassembled and cleaned the rods and threaded rods. I checked all the screws and made sure the rods were firmly set in place. Dropped the motors and checked the screws holding the brackets in. Re-assembled and the noise when the nozzle is moving down quickly has gone away. Before I had to loosen the trapezoid nuts before it would move with lower noise. The nuts are now tight and everything appears good for now. Prusa said he's seen things shift in shipping. I haven't printed yet but the machine is much quieter now in Z. I'll update again if my issue comes back.