Err: MINTEMP  

RE: Err: MINTEMP

Test your continuity on you thermistor cables. I have had this issue with both the Mini and MK3s and every time it is a connector or break in the wire.

RE: Err: MINTEMP

Posted by: @stacy-c

My MINI keeps red-screening with "The requ3ested Bed temperature was not reached." It was working fine for months, and now it does this each time.

Things I have tried:

• Different times of day (in case room temperature)
• Window open/closed (in case room temperature)
• Re-seated temperature sensor cable (in case loose cable)

After I re-seated the cable, the self-test ran to completion. However, the first print I tried after that failed within 30 seconds.

Any suggestions on how I might further diagnose this problem or how I might fix it?

The thermistors are sensitive parts and the cables can break easily. I would always keep a bit on reserve. Mintemp or Bed Mintemp are signs of thermistor problems (break, loose contact or defective resistance element).

RE: Err: MINTEMP

It's cold here in NZ right now and my house is 12 degrees C in the morning 🙁 

The printer will not start due to this as the min temp is 18 degrees, a safety feature which prevents the heater elements from starting at all which is irritating, but I appreciate the the safety of using this printer is taken seriously even if a little too much for 'my' liking. 

To get around this, I have successfully pre-warmed the nozzle and bed with a hair dryer for a minute and as soon as the thermistors show 18+C on the screen, you can then pre-heat and be on your merry way with your printing.

An alternative that I tried this morning which was quite novel, was by carefully placing my cup of tea, in the middle of the heated bed and then moved the extruder directly over the top to catch the steam (I know this is an awful idea as steam and electronics are not a good combination, however I was willing to take the risk and will probably not use this method again).

My plan is to make insulation for both thermistors so that during the cold parts of the day, they will hopefully not get colder that 18C and allow me to print whenever I need/want to without getting the hair dryer out.

RE: Err: MINTEMP

Is your MINI from the very first printers which had been delivered?

I think there was an issue with the cover for the cables goint to the heatbed (cover directly on the heatbed) - there was too less space for all the cables and screws and that stuff. They than changed the cover. As already mentioned, it could be a broken thermistor wire / cable. It is also worth to check if the yellow kapton tape is holding the thermistor close to the bed.

What is bed temperature and hotend temperature, when both are cold for longer time period - do they show same temperature or is there a great difference (more than 2 to 3 degrees)

Best regards, Clemens

RE: Err: MINTEMP

@clemens-m

Thank you for your suggestions.

This is certainly one of the early MINIs. Not the very first, but pretty early. I had the connector apart before, but hadn't noticed the thermal sensor wire went through it. I took it apart just now and I see it. It's reasonably tight, but not cramped. The wire does not appear to be crimped. I'm guessing I don't have an early-early one then.

The tape appears to be securely holding the senor to the bed. There's no give. I ran my finger over it to flatten it anyway.

After much drama, I found my continuity tester. When I remove and test against the connector to the PCB board the needle jiggles, but it does not sound off.

In power-on state, after being idle for a while, both the bed and hot end show a similar temperature (22-23). I'm in the northern hemisphere (Boston area) and it's been plenty warm.

I did a filament removal just before doing the above tests. The bed happily went up to 60 degrees, and held steady there while I removed the filament. 

After re-assembly, I ran the self test. And it aborted after about 20 seconds with Err: MINTEMP, Bed temp: 27/35. Sometimes, though it passes the self check.

So, if the thermal sensor is bad, is this the part I order: https://shop.prusa3d.com/en/mk3mk3s/951-heatbed-thermistor-e3d.html

I didn't see any instructions on how to replace this on the MINI. It wasn't part of the original assembly. Any suggestions for that or does anyone have any experience?

Many thanks for any and all help!

RE: Err: MINTEMP

@stacy-c

I would say that your MINI should still have warranty. So the typical way is to login with your user account to the shop (same you used when you bought your printer) and wait that the small window "chat" appears on the right bottom corner of your display. Then start a chat and describe your problem. They will guide you trough the process to find the defect part and normally will send you the spare part for free (if it is under warranty).

Best regards, Clemens

RE: Err: MINTEMP

@clemens-m

Thank you. I talked to support, and we did a number of other tests. The upshot is they will send me a new themistor. Since other people may search and find this thread, I'll include some of the other tests they had me do.

Rather than a continuity test, I was asked to do a resistance test across the heatbed. There are some very helpful instructions here, along with expected values:

https://help.prusa3d.com/article/mvzxcjkvtx-troubleshooting-multimeter-usage

I was asked to reflash the firmware back to 4.0.4 to confirm that it still failed there.
I also was asked to watch the temperature, and then jiggle the cable at the thermistor end, where it joins the heatbed, and at the PCB, to look for changes.

I measured the resistance across the thermistor, which should be roughly 100K Ohms. The exact value depends on the temperature (since that's what it does). Mine was around 80K for around 22 degrees.

 Lastly, just to confirm it wasn't the other thermistor, I wigged that too and watched the results.

Thank you, everyone, for your help. Hopefully when the new one arrives it won't be too hard to install and will fix everything.