Bed Thermistor - failing - MINTEMP BED - known issue?  

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

Guess that's a paid feature?  see attached.

I didn't have any problems printing with PETG Prusament and the .20 Quality preset in PrusaSlicer.  Just remember to split the tube in the slicer and put the split face on the bed.  Note that the modified cable cover and tube may not be a rigid assembly--I haven't seen a need to make it one so far.

I've done about 20 full-bed prints since my last post, and the cable seems to be holding up pretty well (for now...)

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

Interesting!  I knocked up something similar in terms of supporting the cable at the heatbed end with a 90-degree tube.  Not as elegant as yours - I just created something that slid onto the existing covers where the cables meet the heatbed.

One question - if the cables now exit the buddy board box at the back, is a 90-degree bend at the heatbed required - or even desirable?

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

After performing 2 sensor replacements in 3 months and finding that the short was near the heatbed clamp both times, I decided to recharacterize the cable motion.  Just making a portion of the cable rigid would also keep the cable from hitting an enclosure, but the overall cable motion is still a flex so the failure mode hasn't changed.

Without the tube in the new configuration, the cable would still endure a flex focused at the heatbed clamp.  With it installed, there is arguably still some flexing motion in the arrangement, but it is minimal by comparison.  

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

Good points.  I've printed most of your design, which by some coincidence has exactly the same dimensions as mine.  Although I'll probably stick with my tube as I put in 3 30-degree bends in the space of about 20mm rather than a single 90-degree bend.

Although my replacement thermistor arrived today, I haven't experienced any more failed prints since installing my "mark 3" cable support 🙂 

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

Interesting idea.  I fought through this on my Mk3S.  

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

I built a cable chain for my Mini and so far it works fine.

prusa mini cable chain

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

Posted by: @mgtarallo

Hi Guys - just curious how many of you have experienced bad thermistors?

I love Prusa's printers - I have 2 MK3s - both of which have had failed Thermistors at different times. BOTH replaces under warranty. Support has been great. I inquired if they are doing anything about this, being it seems to be a known issue. Even though the wire seems fine, testing with a multi-meter reveals it is not.

I even made a video here to send to Prusa:

https://fb.watch/2Y81Ln0PND/  

After replacing it - ohms read consistent 124 - and I have had 4 jobs complete already.

If you guys have some creative solutions to prevent this, I'd love to know about them

Thanks and stay well.

 

 

My thermistor cable started failing yesterday when the bed moves back.

I had been printing fine in the morning with no signs of a problem and I tried to set a new print going and then I got the warning message.

The videos shows it only does it when the bed moves back and the temp drop at roughly the same point when the y axis moves either by hand or during a test.

I am contacting prusa support shortly.

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

https://www.dropbox.com/s/iizoz6cix9nktro/self%20test%20edit%20showing%20temp%20drop.mp4?dl=0

https://www.dropbox.com/s/jxiz9eo5mdyyvj5/manual%20x%20axis.mp4?dl=0

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

I recieved the replacement heat bed thermistor this morning by DHL, I wasn't expecting to get it so quick so big thanks to Prusa support and the the agent who dealt with my problem.

now to read through the online knowledge base guide before I dismantle things.

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

Its been a year since the last post in this thread, so there should be good run time on possible solutions:  A) Modified strain relief (angled wire guides) at the bed-end; B) e-chain, and C) silicone wire replacement.  (did I miss any solutions?)

Questions

1)  Is your solution still working?

2) What else should I expect to fail on my MINI?  Is the bed thermistor by far the most common failing component?

I have a bed thermistor on order, but I suspect that the problem is wire fatigue, and changing out the wire would be the best move. 

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

I keep a stock of flexible silicone wire in 24AWG, for replacing thermistor wires, Motor wires, pinda wires, fan wires and filament sensor wires. (Various colours Red ,Black, Yellow ,white  green and blue will probably be enough colours. don't forget heatshrink tubing, soldering iron, solder and zipties...
I also keep 16AWG for heatbed power and extruder heater wires. (RED and Black) 
I don't need to use them frequently, but they are available when I do need them

As I said, you probably won't need them frequently, but they are handy to have on hand. 

Nozzle thermistors and heaters are also useful to have 'in stock'!

Joan

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

Posted by: @cjnaz

Its been a year since the last post in this thread, so there should be good run time on possible solutions:  A) Modified strain relief (angled wire guides) at the bed-end; B) e-chain, and C) silicone wire replacement.  (did I miss any solutions?)

Questions

1)  Is your solution still working?

2) What else should I expect to fail on my MINI?  Is the bed thermistor by far the most common failing component?

I have a bed thermistor on order, but I suspect that the problem is wire fatigue, and changing out the wire would be the best move. 

 

Mine is still working at 2 years.  Between it and the part cooling fan, these are the two most common replacements for me.  

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

Posted by: @cjnaz

Its been a year since the last post in this thread, so there should be good run time on possible solutions:  A) Modified strain relief (angled wire guides) at the bed-end; B) e-chain, and C) silicone wire replacement.  (did I miss any solutions?)

Questions

1)  Is your solution still working?

2) What else should I expect to fail on my MINI?  Is the bed thermistor by far the most common failing component?

I have a bed thermistor on order, but I suspect that the problem is wire fatigue, and changing out the wire would be the best move. 

 

1) It is wire fatigue;  the chance of bed wire failure is greatly increased in enclosures where the bed wires impact a side (mine is a touch over a 17" cube.)  I haven't had any new wire issues since creating/installing the angle tube and modified board cover, having minimised the amount of bend/flex the wires are subjected to.

2)  Another potential source of grief is the heatbreak.  Because of the design compromise to make the printer more-affordable, the tube OD does not have a pinched-in section above the heat block, so heat creep will cause the ptfe tube inside to melt/shrink/constrict over time, causing filament feed issues.  ABS/ASA and other high-temp prints will accelerate the failure timeline.  Bondtech sells a replacement heatbreak, though I hadn't seen much news regarding long-term effectiveness.  

The alternative is to replace the hotend.  E3D and Slice Engineering offer replacements; I went with the SE Copperhead for my light-duty needs and very minimal impact on print volume/geometry.  (There's a thread regarding all this; I didn't post in it and it's been too long so the location dropped off my browsing history.)

Optional mods:  Bondtech extruder with filament sensor.  Bed leveling mod

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

The new parts:  https://a360.co/2Ycb4i5

@Mr.Shaky,

I'm functional in F360, but I can't figure out how to download the models for these parts.  Clicking on the link brings up a markup view in the browser.  How do I either download the model or open this in F360 itself?

Thx!

RE: Bed Thermistor - failing - MINTEMP BED - known issue?

I too caused my own pain by building a box and continually running the heatbed cable into the back of the box.  I found the break in the thermistor wire right at the cable strain relief at the back of the bed.  I've done two things to "fix" the issue:

1. Replaced the thermistor wires with high strand count, silicone jacketed wire.  This wire should do much better with long term flexing.
2. Eliminated hitting the back of the box and eliminated tight bends by replacing the cable strain relief with this design.

Ask me in another year on how well all of this is doing.  :>

RE:

Just to add to this; I got my Mini+ two weeks ago directly from Prusa.  Today my thermistor/cable shorted. It failed in the middle of the night, woke everyone up with the alarm.   Bummed to see so many with this issue and it seems to be pretty widespread.  Hopefully I can get a replacement part soon.

The kicker is that my Mini + had been printing beautifully!  Replaced the nozzle with an E3D Nozzle X and have been printing CF PETG, it’s amazing stuff.