Board or thermistor problem? Prusa reads low when above 150 C
 
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Board or thermistor problem? Prusa reads low when above 150 C  

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Alan Ableson
(@alan-ableson)
Active Member
Board or thermistor problem? Prusa reads low when above 150 C

My hot-end has started running hotter than the LCD display is showing.  This happened after cleaning the hot end with a brash brush and hearing a sparking noise from the EINSY Rambo enclosure. 

  • @ 210 target, I got a lot of smoke from the burn-off of old filament, indicating a temp well above 210 (this was the first sign of the problem, so I shut down before I thought to test with a thermometer).
  • Comparing the LCD temperature display with an instant-read thermometer shows e.g. 180 target + actual on the LCD, but the thermometer reads ~210 and fluctuating up and down by up to 10 degrees.
  • @ 170 target + actual on the LCD, the thermometer reads ~185 and fluctuating up and down by up to 10 degrees.
  • @ colder temps, 150 target and below, the LCD target, LCD actual and the external thermometer all read the same, +/- 2 C.

This same behaviour is happening even after switching between two thermistors, one originally installed, and a new replacement unit. 

Questions:

  • Are there any other troubleshooting tips for the real vs measured temperature?
  • Is the board the most likely candidate for replacement or could the cause be anything else?

Any advice is welcome!  Thanks,

Alan

 

Posted : 03/06/2020 2:59 pm
Alan Ableson
(@alan-ableson)
Active Member
Topic starter answered:
RE: Board or thermistor problem? Prusa reads low when above 150 C

Resolved!

The extruder uses the T2 pins for its thermistor connection.  T1 beside it is not used though, so I thought I could use T1 instead, leaving a damaged T2 unused.

I downloaded the Prusa firmware from github, and the Arduino 1.8.5 (needed!  Compiling failed with the current Arduino 1.8.12).

I followed the instructions for Windows in the README in the package, and was able to compile the vanilla MK3S firmware, and update the printer.

To enable the switch between T1 and T2, I edited pins_Einsy_1_0.h  I'm definitely a novice on editing these, so take with a grain of salt but it looked like:

  • T0 on the board is used for _BED, so it had to be ignored.
  • TEMP_0_PIN 0 :  TEMP_0 is really T1: key thing is to keep the pin '0' for what I want.
  • TEMP_1_PIN 1: this is what currently points the extruder temperature measurement at T2 on the board.

I swapped the pin numbers here to get:

TEMP_0_PIN    1

TEMP_1_PIN   0

I compiled again and flashed the new firmware to the MK3S and it seems like the fix worked! 

  • Initially, there was a MINTEMP error, because the thermistor was still plugged in to T2, but the firmware wanted to read from T1 which was disconnected.
  • I shutdown and moved the thermistor wires to T1.  Booted up and had temperature readings!

Using the new pins, the temperature readings matched those on an external thermometer, and I was able to run the PID calibration at 210 C and have it stay around 210 instead of spiking. 

 

Posted : 04/06/2020 5:36 pm
Katony
(@katony)
Active Member
RE: Board or thermistor problem? Prusa reads low when above 150 C

Excellent instruction did the same... after burning out slot because heating the hotend so i can swap the nozzle. cut the thermister cable and blew out the board. swapped thermisters didnt work so board was fried... (only update Arduino and Arduino IDE means the same thing). Also getting a mosquito hotend so, i can swap hotends without having to heat the hotend.

 

Posted : 19/06/2020 10:25 pm
Alan Ableson
(@alan-ableson)
Active Member
Topic starter answered:
RE: Board or thermistor problem? Prusa reads low when above 150 C

@kumkatony

Thanks: yes, I should have said "Arduino IDE 1.8.5" in the note!

Posted : 23/06/2020 1:22 pm
Mirage Visualisation
(@mirage-visualisation)
New Member
RE: Board or thermistor problem? Prusa reads low when above 150 C

Thank you for the information. It was really useful and now I can use my spare port instead of buying a new board. 

Thanks also to this guy who made a video which helped me compile the code super easy -

Posted : 01/10/2021 12:56 pm
SitiNurbaya
(@sitinurbaya)
New Member
RE: Board or thermistor problem? Prusa reads low when above 150 C

thank you thank you thank you! i swap heatbed thermistor to number 1, you saved my money!

 

Posted : 17/11/2021 2:19 pm
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