I had the issue with my mini recently described in this thread: viewtopic.php?f=43&t=3415&p=21912&hilit ... air#p21912.
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.
1) Remove controller cover w/ small allen key - 6 screws.
2) Unplug Fan 2 plug from rambo board (the fan atatched to the cover being removed).
3) Unplug large 4-wire plug for secondary controller board (the board attached to the cover being removed).
4) Set controller cover aside.
5) Unplug small 2-wire connector labeled "Y-MIN" at the bottom right corner of the rambo board.
6) Unplug red wire from rear Y-limit switch under the bed.
7) check continuity from rambo end to bed end of red limit switch wire.
**If continuity exists, replace limit switch. If not, proceed...
8) 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)
9) Clip zip ties securing the wire set in question.
10) 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.
11) Pull wire back through the tank track guide from the bed side.
12) Cut new length of wire 1-2" longer than the removed wire.
13) 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.
14) strip new wire ends and connect original connectors to new wire via butt connectors and heat shrink.
15) Connect female spade end to the y-limit switch.
16) feed red wire back through the tank track guide. Its tedious but you can do it. Tweezers help.
17) reinsert pin into two pin connector at rambo end.
18) Plug connector into rambo board at the "Y-MIN" location.
19) Plug in secondary board and Fan 2 connectors.
20) 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.
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