I had the issue with my mini recently described in this thread: https://forum.lulzbot.com/t/y-axis-limit-fail/2950/1
After reading that thread a couple hours ago I checked continuity of the red y limit switch (the one on the back side of the bed) and found it to be broken internally about 3" from the bed end connector.
I replaced the wire and all is well. Repair procedure and attached reference pics below:
*Before you go any further, unplug the red wire from the rear y-limit switch under the bed and see if your symptoms change. If so, you have a different problem. If not, proceed…
Allen key for controller cover
Multimeter with continuity function
Needle or pointed multimeter probe
~18" length of 18ga red stranded wire
Two 18ga butt connectors
1-2" length of heat shrink wrap
Pliers for crimping butt connectors
lighter for shrinking heat shrink wrap.
- Remove controller cover w/ small allen key - 6 screws.
- Unplug Fan 2 plug from rambo board (the fan atatched to the cover being removed).
- Unplug large 4-wire plug for secondary controller board (the board attached to the cover being removed).
- Set controller cover aside.
- Unplug small 2-wire connector labeled “Y-MIN” at the bottom right corner of the rambo board.
- Unplug red wire from rear Y-limit switch under the bed.
- check continuity from rambo end to bed end of red limit switch wire.
**If continuity exists, replace limit switch. If not, proceed…
- Remove plastic wire shield from the set of wires going to the bed (the ones going through the wire guide that looks like a tank track)
- Clip zip ties securing the wire set in question.
- de-pin the red wire from the connector on the rambo end. You can use a needle or the probe from your multimeter to press the spring tab and pull the pin backward out of the plastic connector.
- Pull wire back through the tank track guide from the bed side.
- Cut new length of wire 1-2" longer than the removed wire.
- Cut off original connectors from broken wire about an inch from their respective ends. If you happen to have those connectors on hand you can just make a new wire. I didnt and I didn’t want to get them, so I reused the originals.
- strip new wire ends and connect original connectors to new wire via butt connectors and heat shrink.
- Connect female spade end to the y-limit switch.
- feed red wire back through the tank track guide. Its tedious but you can do it. Tweezers help.
- reinsert pin into two pin connector at rambo end.
- Plug connector into rambo board at the “Y-MIN” location.
- Plug in secondary board and Fan 2 connectors.
- Install controller cover. PLug in printer. Test Y home function. Rejoice.
All in, having never done it before and taking pics it took about 30min. Solid 3 on the difficulty scale.