Mini 1 min bed temp error when printing - bad wires?

Out of no where my Lulzbot Mini 1 has started giving me a mintemp bed error when starting prints. I can leave the bed on at 60 for half an hour or more and it’s fine and rock solid - but the moment I start a print - it gets maybe 30 seconds into the first layer and then halts.

I’ve tried firmware flashing to the latest FW successfully - but the problem still persists with every print I try (6 in a row now). Since the bed is stable in octoprint’s graph without any dips or temp changes while sitting still - I’m guessing there’s a short in my wires (two big purple ones maybe?) that are losing connection when the bed is in motion.

I do not see any wires in the parts store and wasn’t sure the best way to go about taking all of this apart and troubleshooting it. I believe I have a continuity tester somewhere at home, but since the bed heats fine - I’m guessing continuity will be fine until the bed moves… is there any guides to replacing these wires and is there a default harness to purchase with all the wires in a bundle or such?

If I’m off base here and it might be something else - I’m open to suggestions too. Many thanks!

With everything off, just check for continuity and wiggle the wires to simulate bed movement. Having a tester with audible feedback on continuity is a big help.

What happens if unload the filament, then simulate printing with bed heat set to off?

Who would take out the filament and simulate a print with the bed temp set to off? What kind of crazy person are you? :slight_smile:

I’ll give it a try. :wink:

If the print job is set to bed temp off - does that mean it will go unmonitored? Or will it still freak out if it just loses communication to know what the temp is?

Since it appears to be reporting the heat and heating correctly, setting it to 0 should hopefully let it try and print while taking the bed out of the equation. It might still halt and throw errors.

You can also see what happens when you manually heat the bed, then send manual bed movement commands.

It appears to be going fine with the bed set to off… I can see the temp readout in octoprint and see several dips where it is losing communication with the bed. So Most likely this is the wire as I suspected - any tips on replacing that wire? (Big purple ones I’m guessing?)

Try and determine where the break in the thermal sensor circuit is. It could be a break in the wire between the harness and sensor, or at a harness.

Once you’ve determined where the break in the circuit is, it shouldn’t be hard to fix it. If it’s the thermal sensor itself going out, they’re not terribly expensive, just make sure you get the right one.

To expand on what @Wrathernaut has said, there are two components (i.e. two sets of wires) for the bed. One is the connection to the heater (big purple) and the other is the connection to the thermistor which provides the temperature feedback.

It is more likely that the thermistor wiring or the thermistor itself are to blame for this behavior. On my TAZ 6, the heater and thermistor are firmly attached to the plate (see below). Also examine the connectors and the wiring harness.

The Mini’s are known for breaking the purple heater wires for the bed. When I replaced mine I kept them outside of the drag chain to reduce the bending. Maybe if they were replaced with silicone wires they could handle the bending in the chain. I don’t think silicone wires were a thing back when the Mini was designed. Just goes to show that as nice as a drag chain is for wire management you can still bend it too tight, especially for bigger wires.