Got the MINTEMP Error Blues

[BryanD]

This is happening more and more frequently (from Cura console):

< [17:04:19] ok N753 P0 B3

< [17:04:21] T:245.00 /245.00 B:89.21 /90.00 @:73 B@:127

< [17:04:21] echo:busy: processing

< [17:04:23] ok N754 P0 B3

< [17:04:23] ok N755 P0 B3

< [17:04:24] T:245.00 /245.00 B:90.10 /90.00 @:72 B@:23

< [17:04:25] echo:busy: processing

< [17:04:26] ok N756 P0 B3

< [17:04:26] ok N757 P0 B3

< [17:04:27] T:245.10 /245.00 B:89.90 /90.00 @:70 B@:71

< [17:04:28] echo:busy: processing

< [17:04:30] T:245.10 /245.00 B:90.14 /90.00 @:72 B@:0

< [17:04:30] ok N758 P0 B3

< [17:04:30] ok N759 P0 B3

< [17:04:32] echo:busy: processing

< [17:04:33] T:245.42 /245.00 B:89.83 /90.00 @:64 B@:57

< [17:04:34] echo:busy: processing

< [17:04:34] ok N760 P0 B3

< [17:04:34] ok N761 P0 B3

< [17:04:36] T:245.21 /245.00 B:89.87 /90.00 @:71 B@:87

< [17:04:36] Error:MINTEMP triggered, system stopped! Heater_ID: bed

< [17:04:36] Error:Printer halted. kill() called!

I don’t get it. What does it see that it doesn’t like?

[arjun_dayal]

I believe your heatbed thermistor either has a loose connection or is broken. Check your control panel for any loose connections. If you don’t find any, you’ll probably have to replace your heatbed thermistor.

Basically, the thermistor is the wire that transmits temperature information to the control board. If it’s broken or loose, the control board can’t detect the bed temperature, thus the error. If you keep trying, you run the risk of having your bed continuously heat up and not stop because of that faulty wire.

[BryanD]

Yes, that was my first assumption too however the console shows the temperature being reported as stable. My thinking is that the host computer wasn’t aware of any issue. Is there a local software circuit in the Rambo that monitors the thermistor?

[arjun_dayal]

I don’t believe that there is any type of circuit in the Rambo that keeps track of the status of the thermistor. I’ve had the same MINTEMP issue on my Prusa MK3 (actually have it now), and it has the same thing as your Lulzbot where the console says the temperature was fine. One thing you can do is use the cura software to monitor the bed temp. Use the pre-heat option in the Cura software to heat it up slowly to 90 degrees C. I’d recommend getting there in increments of 15 degrees and holding the bed at each temperature for 30 minutes. If any time, you return to the printer to find that you have the MINTEMP issue, it’s most definitely the thermistor.

If you don’t get the MINTEMP issue throughout this whole process, then I honestly have no clue what else it could be. You might want to try replacing the entire bed, but I have an innate feeling that won’t really help your situation that much.

[BryanD]

I wish there was a quick way to understand how the MINTEMP error is triggered. Is it a function of the software running on the host PC or is it running inside the Rambo board? It seems like there is some kind of higher sampling rate than what is showing in the console, which makes me believe the Rambo is involved in shutting it down. This Mini was purchased used and had many bad wires in the printbed snake. I guess its possible that the thermistor wires need to be replaced as well? Ever see a problem with degradation of overused wires for the thermistor result in MINTEMP error on a Mini v1.03 ?

[b-morgan]

The MINTEMP error is triggered by the firmware running on the Rambo board.

It is the nature of the beast that when there are electronics that move, the wiring required by those electronics is subject to repetitive stress and can fail. Add to that fairly large temperature changes and this is a not so friendly environment!

These failures are either catastrophic (i.e. wires break) or intermittent (i.e. cracks in insulation, breaks that are partial and/or dependent on position).

I would carefully inspect each wire in the harness and if necessary, replace any that are suspect. This would include the thermistor wires.

In an ideal world, one could buy a replacement wiring harness, but things are nowhere close to ideal these days.

[BryanD]

Super helpful! Thanks! I will try to find a new wiring harness.

[BryanD]

Yeah, it would start and then fail after 15 minutes, then 5 minutes then 1 minute and now it only gets to the first “left turn” then dies a MINTEMP death.

[allarson]

I had this problem and fixed it by replacing the cable. When I did so I discovered that
the installation of the cable violates a cabling rule used in the old Bell System, NASA,
and other large systems companies, back in the days when systems were large
racks of electronics cabled together. ( yes I’m an old engineer). The rule is

PHYSICALLY ANCHOR EACH CABLE NEAR THE CONNECTOR

The bed end of this cable floats free, and flexes as you print. That is the root cause of this problem.

My solution was to use the little stud bolt on the bed where the black wire attaches to
mount a small metal cable support made from a grounding lug with a ring soldered to it.
Then I used a zip tie to anchor the cable. Now when I print, the cable does not move.

[Derek]

Can you include a picture of the setup? I’ve hand my harness fail twice and I wouldn’t mind taking extra steps whiles it’s working good to make sure it lasts.

[allarson]