Y Axis Limit Fail?

Had a curious problem this morning. I had a print finish overnight. Removed it from the print bed and went back to control to start another print. Moved X and Z to home position, but Y would not stop at home and the motor kept turning. Had to shut off the machine so as not to strip the belt. Figured the stepper index got corrupted somehow, so powered it back on to see if it reset the motor. Same problem.

What is the limit switch / part I need and is there a video or something somewhere that demonstrates the repair? OR am I completely wrong in my assumption of the problem? Is there somewhere else to start?


Check to make sure the metal tab on the switch for the back Y motor mount has not fallen off. It is on the bottom of the heat bed on the belt clamp.

Everything seems to be intact… although I am really not sure what you are asking me to check. A picture would help… can you attach? There is a grounding tab? at the end of a wire that comes from the wiring harness that connects to the plate. The spade connectors to the switches are firmly connected. I see no other metal tabs or areas that look like they are missing a metal tab. I have found nothing of the sort under the unit. There is no contact plate for the switches to activate against. They actuate against the guide bar pillow block face. Both the front and back limit switches are showing continuity when I trip them. I see no reason for Y travel to not stop when it reaches it’s zero reference point.

I really would like my machine back up and running… any help would be greatly appreciated.


I just check a Mini sitting here, and they do not put the lever on the Y switches. So your RAMBo probably died. They are very sensitive to static on the limit switch inputs. :blush:

Ok… quick search online yields many possible options from $90-150. Is there an official Lulzbot spec for it? I really don’t have the time/interest to source it and play the buy-parts-online lottery right now. I need my machine back up and running as quickly as possible… if it ain’t turn’n it ain’t earn’n!

*** Any help would be greatly appreciated ***

It would be REALLY nice if there was a support page / web store to buy any/all replacement parts for their printers or for a DIY build… lucrative opportunity for Lulzbot if anyone on that end is trolling this. Doesn’t seem like it would be outside their charter. Wonder why they don’t…



They have a reasonable selection of parts. I’m surprised Lulzbot doesn’t offer a full parts inventory though. They give you part numbers and sources etc, but it would be nice if we could just get them direct.

If it were my printer, I would check the limit switch itself with a meter, then the pins where it connects to the control board. Just to rule out the connections and the switch itself. If those are good, try manually triggering it and see if it reports that it hit an endstop. I think it will display in the Cura printer control window. I don’t think there’s anything else to go wrong there other than the control board.

The Rambo doesn’t have input protection? Even a debouncing capacitor would help in they are that sensitive to noise on the digital inputs.

…on that note, if in fact the RAMBo is the problem and static is the likely root cause, is the unit just not adequately grounded? Are additional grounding precautions prudent?

The operating environment I have it in is not overly dry or humid… it’s in an active basement workshop area with good airflow and forced air heat. If anything my concern is more ambient humidity impact on the spool of material that is hanging in open air while it is printing.


Seems we were both typing at the same time… 8^)

I will do a full survey of the connections again. The switch works.

I will also check out the link… thanks! -john

Your limit switch likely pulls the signal to ground when activated. You should be able to measure a voltage, probably 5V ?, across the switch if it isn’t closed, and the machine is on.

My guess is you had a wire break in the Y axis flexible harness under the bed.

Lulzbot might want to look into finer stranding of wire for these machines since the wire is constantly flexing. I don’t know what they’re using, but if it’s 7 strand, it will fail a lot sooner than 19 strand.

Good Luck, and let us know what you find. Me and my mini will appreciate it.

Much cheeper fix than a new RAMBo… definitely worth checking out first. Thanks for the suggestion. I’ll let you know what I find.

I’m building my own mini from scratch, and the y-min and y-max limit switches are what i recently finished working on.

My guess is that the wire has a break in it. Most likely cause of failure. Especially since it is a moving part being flexed back and forth. I say try ohming out each wire. Also try flexing them while you do this. It sounds like ohming out the switch seems to have shown that the switch itself is still good, if that’s the case then it suggests either a wire failure or a board failure. I personally think a board failure is unlikely, but i don’t have much experience with the rambo boards yet.

The limit switch parts can be found in the lulzbot BOM here:

But any old mini limit switch will do. They just not might fit your little spade connectors, in which case you would need to solder the wires to the posts. Another possible problem is at the other end of the wire at the little black plastic connector. It is possible that one of the metal crimped pieces came out of the plastic header. But that seems unlikely too. But it’s worth checking.

in the end if it is indeed the board and nothing else perhaps contacting lulzbot support can get you a replacement if it’s under warranty.

Time being a scarce commodity for me these days, I unfortunately have not followed up on your excellent suggestion yet. I greatly appreciate your post and apologize for not acting on it sooner and reporting back. I really hope to play around with it this weekend. Never got any answer back from Lulzbot on whether or not this was covered under warranty or not. Contacting them directly for support is not exactly clear.

While pricing controller boards as a backup plan, assuming the worst, I came across https://pinshape.com/blog/4-interesting-3d-printer-controller-boards/ which got me thinking and wondering if anyone else has done a brain transplant on the Mini with a different controller board than the MiniRambo? If I have to bother with buying a new controller, I could potentially save $50+ and upgrade the output quality by going with a better RADDS v1.5 3D Printer Controller instead. Easy to consider when you have no idea the consequences however. No idea if it is compatible with the steppers on the Mini. No idea if common connectors. No idea if I can still drive it with Cura, Makertbot, or Simplify.


I had this issue described above with very similar symptoms (y-axis seek to extent would not stop upon hitting endstop). The cables for the endstop sensor in the cable chain were replaced in RMA by Lulzbot and it cured the issue for me at the time.