The temp reading on both of the extruders will jump around by up to +-8 degrees. And it's not just a display error, as the heater LEDs show that the heaters are responding to the displayed temperature. Here's a video (Google Drive):
https://drive.google.com/file/d/1GgET7q ... sp=sharing
At first I thought it might be an EMI issue in the thermocouple signal lines, but that both readings jump simultaneously and in the same direction seems to indicate... something else.
Here's a list of things that I have tried:
- Replace thermocouple
- Replace extruder connection board
- Replace hotend
- Insulate hotend
- Add a capacitor across the thermocouple terminals
- Swapped left and right extruders (nothing changed; they both do it)
- Updated firmware (currently 1.1.6rev1)
- Updated touchscreen software (currently 0.9.2.1026)
- Stared vapidly at the control board for an hour
I'm out of ideas. The only thing I haven't played with yet is the control board. It may be worth noting that this particular printer came with the controller board's blower fan plugged into the HE2 (heater 3?) port, causing some overheating issues early in its life.