Mini Autolevel Gone Wild

My Mini has decided to stop autoleveling. When the Autolevel sequence begins it goes to the first corner and instead of starting down it retracts the Z axis and goes to the second corner retracts again then the third corner and fourth corner as well. Then with the nozzle about 50mm over the bed it begins to print in thin air. I suspect there is a short somewhere which tells the leveling system that the nozzle is in contact with the washer when it is not. I have heard that there are several issues tht can cause this to occur. Where can I find a wiring diagram and connector pinout ? How can I tell whether the main board has been damaged by heater current to the Z limit?

With the print head not touching any washers, send the printer a M119 command and review the response. Based on your symptoms, I expect you will see Z-Min in a “triggered” state. That means either the board is bad, or a wiring problem.

If under warranty, you may want to leave the rest to Lulzbot because if you accidently damage anything else doing the next few steps, it could void your warranty.

Turn off and unplug the printer. Open the control box, and locate the molex plug for the Z-Min end stop. (Consult the Lulzbot OHAI assembly instructions if necessary, but as I recall the sockets are identified on the board.) Disconnect the plug connected to the Z-Min socket.

Close up the control box, plug in and turn on the printer. Run the M119 command again. If the Z-Min still shows “triggered”, then your mini-Rambo board is bad. If Z-Min now shows “open”, then you have a wiring problem (short) in the Z-Min wiring.

THanks !!
Looks like I don’t need a mother board one of the thermistor wires was shorted to the head. Your procedure was very helpful in diagnosing the problem. Machine is well used and out of warranty but thanks to open source docs and this forum its back running.

Glad you got it fixed! And thanks for reporting back… I didn’t know a thermistor wire short would cause those same symptoms - great to have it documented here on the forum for future. Happy printing!

Still having issues with autolevel but behavior is different now. The thermistor short was definitely the cause of the first issue. Now after issuing a G29 to the printer it starts its autolevel sequence comes down rapid to touch the first pad retracts then touches back down slowly finds the washer, retracts and proceeds to the second washer it comes down rapid, touches the washer and retracts then cleans the nozzle and starts over. It acts like it did not contact the 2nd washer at all the nozzle is clean and makes good contact. Any clues?

Check that the X-carriage rods are parallel to the bed. Measure from the bed (left and right edges) up to the lower x-axis rod. If it isn’t parallel, turn off the printer and turn one of the z-axis rods by hand until the x-axis rod is parallel to the bed.

Then turn the printer on, home all, and try another print.

Particularly if the right-hand side is “high”, the head needs to travel downward too far “looking for” the washer touch. If it starts too high, the firmware can “give up”, thinking it has gone down too far and deciding the nozzle is dirty, initiating the re-wipe / re-probe process. Making sure the x-axis rod is parallel to the bed should fix that.

That’s what it was back to printing reliably. What a great little machine. Kind of gladiator got to dig into it a little. Lulzbot does a very nice design job on their parts