I’ve been having a lot of trouble with my mini lately. For some reason I get wild variations in bed temperature. I can’t pinpoint the cause as it seems to be happening randomly. It’s causing a lot of failed prints and wasted material.
Try re-seating the bed heater connection that is zip tie on the bottom of the bed. Then if that does nothing suspect the wires from the C.B to the connector are intermittent. (S.W.A.G!)
But then why would it sometimes have no connection issues at all and the temperature is pretty much level (even opened a window to see if draft affects the temperature a lot), no problems at all.
And then sometimes the print doesn’t even start because the bed failed to heat up, lingering around 40 for a setting of 60.
I use a program that allows me to see the ‘guessed’ power output to the bed heater, so I can see if there is an issue with wiring and such. If it is cooling off and I see it pumping power to the bed at that time I know I have a problem I need to look at.
As for why it works then may not, that is the ‘intermittent’ part of it. Bad electrical connections are the respecter of no one.
New development. I think it’s the thermostat. I’m printing something now, with the bed turned off, and I still have the fluctuations showing up. Going from 30 degrees down to 15. There is no way there’s 15 degrees in my house, so something is going terribly wrong there.
Does no one really have a more definitive answer? This has caused me a lot of damage. Wasted material, time, money and energy.
It is so bad now that even if I print with the bed OFF it can still kill my print (temps drop to 9 degrees celsius sometimes which makes no effing sense!!!). I can’t print anything at all now without the looming possibility that the printer might decide to screw it up.
I don’t want to send this back but if I can’t fix it soon I’ll just send it back in warranty or something…
Yes, my first thought (even without your latest update) was that you have a Thermistor that is going bad but is somewhat intermittent. It’s possible that you just have a intermittent thermistor wire that could be replaced to fix the problem, but it’s more likely i think that the whole thermistor is bad. This might be covered under warranty so you should send Lulzbot support an email to see what they say.
Either way, stop printing things until you get a new bed thermistor and/or silicone heat bed ( i think they have the thermistor built-in) as your just going to frustrate yourself printing with a broken printer.
I have a similar issue with an extruder assembly. I think my thermistor is bad and/or shorting out so i’m going to try and replace that soon.
Warranty is probably the best way to go. But if you want to try and replace your bed thermistor yourself then use this video as a rough guide. https://www.youtube.com/watch?v=jp7ubpbaw-Q
This isn’t a software issue, it is 100% a hardware issue and repair will be required. Its possible this is a loose wiring harness, but most likely its the thermistor. You should consider replacing the bed heater assembly. It works has them fairly inexpensively.
In the meantime while I get my hands on a new heated bed assembly, I think I’ve found a workaround. I edited the Marlin firmware and lowered the MINTEMP parameter to 0. It seems to be printing alright for now.
We seem to have found a solution to a problem similar to what you describe. We have 4 Lulzbot Mini printing exactly the same model. Since a couple of days, one of them shows random problems such as:
Thermal Error, system stopped
Bed temperature instability
Print stops at some point during the print
Since we print a lot, we have to change PEI sheet very often. It is quite difficult to attach bed wires the way Lulzbot attach them and we don’t want to damage those small wires so we let them a bit loose. During print, those wires can sometimes be in contact we the side printer stepper motor. During last print we just changed a little bit the wire position so that they are never in contact with the stepper motor. The bed instability has totally disappeared.
I am suspecting that the side stepper motor is creating an inductive current that is transferred to bed wires when they are in contact. The random information is transferred to the bed wire (thermostat). The controller then reacts with the wrong information; sometimes it detects the wrong temperature, sometimes it triggers a controller shutdown and then stops printing.
If you use your mini a lot, you might have a broken wire between the rambo and the heated bed connection. Replacing the heater bed won’t fix it if this is the case. You need to replace the wiring in the plastic chain that connects to the bed. Most likely it’s the heavy gauge wire that powers the heated bed. If replacing the bed assembly doesn’t do it, replacing the thermistor wires and bed heater wires will fix it. Happened to me back in december. The largest stress in the wires is where they double back in the chain. They get bent over and over again during prints and eventually break.
