Floating temperature values cause overheating of hotend

[thomas-van-der-hout 0]

Hey Ultimaker community,

I've been printing with an Ultimaker original succesfully for quite some time, but a few days ago the following problem started happening:

During printing my temperature drops very slowly and the hotend switches on but temperature doesn't rise. After around 20 seconds the temperature jumps up by a huge amount, as you can see on the screenshot (sometimes even jumps above MaxTemp). Burned plastic also starts flowing out of the nozzle after the temperature jump.

The whole measuring system works perfectly when reading room temperature and when heating up.

http://i.imgur.com/VNY9GOT.png

http://i.imgur.com/EG1TcSj.png

I've searched the internet and did some troubleshooting but the problem still occurs:

 

• Check whether thermocouple still works - Doesn't look damaged and gives good readings.
  
• Check wiring to main board - Wiring between sensor and main board still working.
  
• Check whether it is a software problem - Autotuned PID controller and used different slicers and controllers (Cura, Slic3r, Pronterface, RepetierHost)
  
• Check external interference - there are some dimmers in the same circuit as the printer which could cause voltage peaks, but switching off all of those did not make a difference.
  
• Check thermocouple amplifier board - Everything is properly connected, LED works and sensor gives good readings
  

This pretty much eliminates all hardware and most of the software causes. If the machine loses connection with the sensor the temperature would instantly jump to its maximum or minimum value right? (or is this filtered by the PID controller?).

My last guess would be that the problem lies in the firmware (I'm using The version of marlin that Cura installs, the display shows : 13.03 250000_single).

Do you have any tips/guesses?

 

[gr5 2,224]

This is very unlikely a firmware issue.

It is a common problem to occur on Ultimakers that are several months to a few years old. The quick fix is to switch to the other temp cable. There are 2 cables - one for each nozzle (in case you get the dual nozzle upgrade). For now - just try the other cable (you have to switch both at the print head and also underneath the printer).

UM doesn't properly crimp the wires in the cable at the connector and instead solders them. This is not good because the solder makes the cable stiffer and bending (during movement during printing) can cause these tiny strands to break - one at a time.

Switching to the other cable should help for a few more months. Also make sure you do as good a strain relief as possible. When the second cable breaks you can replace them both.