Update on my blog:
I’m currently in the process of reporting what i believe to be a bug in Marlin firmware. I encountered it when i went to center my new prusa mini bed plate.
Just wondering if you have any info regarding the purpose of the U2 pins shown on this board. I ask because I had problems the bed temperature instability and could find nothing obviously wrong with the wiring or thermistor however while looking over the electronics board I did notice that the plug attached to these pins was almost off because there in no locking mechanism. When I reassembled everything, and after refitting the U2 cable connector, my problem was gone. This may be coincidental and I may still have a wire in the process of failing.
I just looked at a spare mini Rambo board I have. I believe U2 is actually referring to the Atmega chip. But if it is the only connector connected to the 6pin header right next to U2 with no locking mechanism then yes I am familiar with it. If I remember correctly it actually goes to the lower z limit switch and the two pins it is connected to actually go nowhere. It is a dummy port basically. The z-min switch actually goes to the bed leveling probe / hotend. So in essence you have a limit switch that does nothing. Probably coincidental as that was probably not your problem.
I made a big stink about lulzbot continuing to wire up zmin switches if they actually do nothing. Lulzbot no longer even wires them up anymore now.
Honestly though it would be nice to have limit switches for safety. Wiring it to the bed leveling probe seems like a hack to me and not real engineering. But I guess some other 3d printers may do the same.
Thanks for this info. It’s very weird that they wired this and used the wrong type of connector to do it to boot, and yet it has no purpose. I’m guessing it was to do with bed levelling but got superseded by some other method, but never decommissioned. Its confusing because I have no wires below the bed, looking for a place to go. Right now everything is working fine but next time I have it apart I’ll take the time to trace out where those wires actually go.
I am thinking that I should probably order a complete new bed as a backup as although mine is working right now, I have sanded it lightly many times to improve grip. Is Lulzbot the only supplier do you know? I see that they are currently out of stock.
Barry
I think lulzbot has stopped making the old heatbed in favor of the newer 2-piece modular system. https://www.lulzbot.com/store/parts/lulzbot-mini-etched-modular-print-bed-heater
ItWorks3D is a pretty good place to look for lulzbot parts. They probably have the original style heatbed for a decent price. I haven’t used the modular system, but I think I would go that route if I wasn’t doing my Prusa mini flexible bed mod. It would make it nice to replace cracked glass but not the heater. Plus you can flip it over bare glass on one side and PEI on the other.
https://itworks3d.com/product/silicone-heater-24v-170mm-x-170mm-pc-bd0029/
I went ahead and ordered a heater/bed assembled from IT-Works 3D mainly because Lulzbot are out of stock. I’m sure that it will fit my needs for now anyway although I do like the modular idea. Damn shipping is expensive for it though, 30% of the total bill!
Barry
Can anyone with a lulzbot mini check my marlin 2.0 bug for me? I would really appreciate it. Thanks!
My mini came with two seemingly identical print heads complete. In the docs, ‘EO’ = 833. Can you tell me if this value for the print head that it came with it or is it to do with something else? I can seem to find any reference to ‘EO’ in the Lulzbot docs that I have. I am wanting to try the other print head but not sure of the precautions/setup that may be required.
Barry
I’m not sure what EO stands for but 833 is a value I recognize for E-steps. Usually LulzBot would put a sticker with the E-steps value for each tool head on the back of the mounting plate (so you can’t read it when the tool head is installed).
It is E steps. I just couldn’t recall when I was typing:) The spare toolhead has no label on the rear, but I’m guessing that there must be a way to calculate what they should be? I’m guessing it’s a fine tuner for extrusion but not sure
Yeah 833 is pretty close to the calibration for the steppers lulzbot uses. There is a calibration procedure in the OHAI docs if you want to fine tune it.
https://ohai.lulzbot.com/project/extruder_calibration/calibration/
Actually, it’s not the stepper that affects the calibration, it’s the diameter of the hob bolt. Some of the newest tool heads based on the E3D mechanicals start at around 420. The older hexagon mechanicals are in the 800-850 range.
Thanks for this. I will give it a try once I get the Covid stuff under control.
Barry
Just shared my design for new mounting feet for the Prusa Mini heatbed / build plate for my Lulzbot Mini Hybrid conversion project.
Here is the latest update on the Prusa Mini buildplate mod