MINTEMP BED issue  

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LibertyMachine
(@libertymachine)
New Member

Hello all,

I've had my MK3S for about 8 months now, and overall, it's been really good, lot of fun and learning to be had. However, an issue has popped up that I can't quite get past. Lately, it's been giving me a MINTEMP error, print would stop and that's about it. I just did a firmware update, so now it gives me a bit more info; MINTEMP BED error. So it rules out the problem in the hotend, I assume.

What am I actually checking for? The wires don't seem to be broken, the connector is firmly inserted in the RAMBO board. I tried to check the resistance with a multimeter (Klein), but I must be doing something wrong, since my values are all 0.00........

Has anyone else run into this issue and what was your fix?

Posted : 17/09/2020 1:34 am
joan.t
(@joantabb)
Veteran Member Moderator

when your printer is turned on, and at rest, I suspect your hot end shows room temperature, and your bed display on the LCD shows 0C or below 15C
this suggests that    either the ambient temperature is very low, or the bed thermistor circuit is either disconnected  or the wiring is broken. 
with an older printer, the constant back and forth movement of the bed (in this instance) can cause the conductors inside the thermistor wire insulation, to break and go open circuit.  If you can replace the wire for the thermistor from just inside tthe Einsy case, to just under the heat bed, (not polarity conscious)  insulate the joints and with luck you will be back in business. (22AWG will do for the thermistor)
alternatively, replace the thermistor  and it's wiring...   

Please be aware, that the heat bed power wiring has also been flexing, and may also be breaking. I use 16 AWG, Flexible Silicone insulated wire, to make replacement heatbed power leads, in this case polarity is important to ensure the indicator LED lights on the heatbed... Note, you can use 14AWG fo the heatbed if you wish. 

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 17/09/2020 2:38 am
charles.h13
(@charles-h13)
Famed Member

I keep a couple extra thermistors and a hotend around just in case.  

Posted : 17/09/2020 3:30 am
joan.t
(@joantabb)
Veteran Member Moderator

@charles-h13

and a spare heater, and spare wire to make repairs to the wiring...   

Pinda wire seems fragile, I have changed 
Fan Wire seems to generally outlast fan bearings... I try to replace plain bearing  fans  with double ball bearing fans. which seem to last longer.
Touch Wood, so far I have not had a problem with Extruder Stepper Motor Wires. 
Heater wires seem to die when resolving Blobs of doom, or clumsily changing nozzles / clearing blockages
Hot end Thermistor wires then to die during Blob of doom season, either because the Blob rips them out, or because the user, is not careful enough clearing the Blob of doom (I usually use a temperature controlled soldering iron, to gently carve away the excess plastic, knowing that the thermistor wires are so fragile.  In my experience thermistor wires are less prone to damage during nozzle change, than the heater wires.  because they are more flexiblr.
Bed thermistor wires used to get pulled out of place by the movement of the spiral wrap on early printers and this could cause early failure. the move to woven cable wrap seems to have improved this issue. so flexing now causes most failures. 
I have had two heatbed cables fail between my four prusa's, so I now fit Flexible silicone wire during assembly, and since then I have not had any heatbed power wire failures... 

so folks, lets be careful out there, take care to set up your cable management during assembly, and you will reduce the chances of breakages due to  localised flexing. and remember it takes less time to be careful during nozzle maintenance, than it does to replace the heater and thermistor wires... 

Happy Printing. 

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK...
Posted : 17/09/2020 10:31 am
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