z-height moving in the wrong direction

Here’s one for ya. I have an original version of the mini that was working fairly well until I upgraded to the new Cura and Firmware. Now During large prints approx. 40 layers into the print my hot end decides to take a nose dive into my print (like -1 to 2 mm or more). Were not talking loosing a step or two were talking total “Rambo went on a bender and lost its damn mind” kind of failure. Its not a one off either. I’ve got half a 5 gallon bucket of failed prints with the same problem.

I know my description is a tick less than technical but its how I speak. If I couldn’t find humor in this you would be watchin’ me shoot it all to pieces in my backyard on the youtube!! I understand techie I just don’t speak it. Anyway, I’ve gone through the typical troubleshooting procedures. Checked z calibration, e-steps, frame is square and level, x is parallel with y, nozzle and washers are clean, uninstalled and reinstalled Cura, re-flashed the firmware etc…

If I were to put my redneck mind to it I’d say there is something in the firmware/software that is telling this Devil Box to tear up my prints but I’ll be damned if I can put my finger on it!!

Thats where you fine folks come in. I appreciate any and all suggestions that help to get this old fella’s machine rid of whatever is ailin’ it.


The Z driver is under a lot of load(two motors) and does fail in unusual ways due to heat pretty easy.

Also check to make sure if it has the heat sink on the Z driver chip that it is still firmly attached and centered on the chip and not causing a intermittent short.

Thank you Fella, I will check that. I will fire up the Google box, find that critter and report back my findings.

You wouldn’t know offhand what the normal operating temperature is supposed to be would you? Or is the answer not hotter than the surrounding board which just makes sense to me not being that familiar with circuitry? (Sorry for breaking character bye the way…lol)

This Fella may be on to something!!! No I have no heat sinks on any of my drivers :angry: . My board is a mini rambo 1.3a I had to replace it a year or two back due to a power surge. Also is the enclosure fan supposed to run continuously or is it controlled otherwise?

The old firmware ran it most of the time(power is on), while the newer versions run it only while printing/moving the axis.

You should make sure your enclosure fan is plugged into the board properly, it is really easy to accidentally unplug it when working in the board enclosure/power supply area. “Step 19” of the below link shows where it should be plugged in case you aren’t sure.

Also, I’m assuming you haven’t changed your stepper Motor Current Settings. You can check them with the M501 command. You could even drop them in EEPROM using M907 and see if this helps the situation but you really should add the heat sinks back to the drivers as well. My Z motor currents are 1630 (mA) by default. As I said, You could use “M907 Z1200” followed by “M500” to save the changes, for instance in the console and run the print. As long as the Z axis isn’t binding this should let your drivers run cooler, if this fixes the problem you know it was the drivers (and you should make sure you add the heat sinks).

Thank you Mike, I will certainly make sure I get that bugger plugged in when I put back together. I tested the fan with my fancy new bench top power supply and it works just fine so I’m gonna keep an eye on it once I receive them heat sink and get this mess all put back together.

Also I appreciate the other info. concerning the stepper motor current settings. I will check that business as well once its back up and running. Are there down sides to lowering the current settings? Sorry but I’m ignorant to the inner-workings / voo-doo black magic that is motor control.

I’m 50yrs old and have just started to tinker with Arduino / CNC. The hardware side poses little challenge but the software side is giving me a run for my money. I’m trying to teach myself. I have https://www.matrixtsl.com/flowcode/ and all the other tools I need its just a bit hard without fully grasping the fundamentals. I also am a disabled veteran with mental issues that have a tendency to get in the way. :confused:

Kinda off topic but I just wanted to say input from you folks goes 1000x further in helping me understand and learn than any YouTube video or tutorial. Even if it doesn’t help with this particular problem. So again Thank you to everyone so far and to come who contributes, your help is truely appreciated.

You’re very welcome. The only potential downside to lowering the current to the steppers would come if it starts to skip steps (i.e. there isn’t enough torque being generated to turn the motor). If that happened you would know because the motor would be clicking and not turning. Lowering the stepper motor current will cause the drivers and the motors themselves to run cooler. If the heat sinks/fan fix your problem then I wouldn’t bother with the stepper motor currents. If it ain’t broke don’t fix it.

Glad to see you’re playing around with your printer (as someone who can’t help himself either). You know what they say. If it ain’t broke, then you’re not modding it enough.

Hey Folks…

The printer is working great!! The heat sink thing was the problem, (plus the case fan may or may not have been plugged in :unamused: ).

Also I have been having problems with leveling because I messed up the washer mounts. You know the ones where the nozzle touches during auto leveling. Anyway after replacing my PEI sheet I couldn’t get those stupid screws back in so that the washers were level. What a poor design. how did anyone think a washer balancing on a sleeve would last? Anyway I modified the bed corner mounts to fix that problem.
bed_corner_v2.2_Mini v3.png

Thank you all again for all your help!!!
bed_corner_v2.2_Mini v3.png

Glad it worked out for you buddy.