Extruder motor chatters, spins perfectly using other motor control

Prusa i3
New to 3D printing

I'm a Ceramic engineer with the following sliding scale of understanding and aptitude:
  1. Materials
  2. Mecanical
  3. Electrical
  4. Software (Fortran...I'm old)
  5. Extinct languages
  6. Flying under my own power and last on the list....
  7. Electronics
Honestly, I understand the concepts, but struggle with the magic pin-things soldered on the boards.
All that said...

Here's what's going on:
  1. Printing just fine after initial assembly and setup (voltage pots set to 550 mV)
  2. After a long run of many successful prints I get what appears to be a normal clogged nozzle, no biggie
  3. Take the hot end apart, heat it up, clean out the feed tube, scrape off tip...
  4. Put it back together and fire it up
  5. Extruder motor chatters and does not feed
  6. Take it apart again, heat it up and, without reassembly, manually cycle the motor...chatter.
  7. Bump the pots up to 700 mV to increase the torque.
  8. Repeat #6 with the same result. 
  9. Connect the X motor controller wire to the extruder motor. Manually fire X up, motor works like a charm.  Lots of torque, agrips the filament...all good.
I'm trying to spin the motor without the hot end attached and without filament I've eliminated a clogged nozzle issue. Given that the motor runs well using the X control, I believe I can rule out a bad motor.  With the voltage pots all up to 700 mV, I don't think it's an under-power issue....the other motors spin well.   The hot end reaches temp fine, and the motor does "move", so I think the temp sensor is reading fine.  That leaves me with the electronic bits between the extruder voltage pot and the motor.  That's where I am out of my element.  I guess it could be the software, but I've been running great for months and haven't changed anything (and wouldn't know what to change it to if I did).

I patiently await the guidance of the masses.


  • Firmware prevents any extruder motor moves if the hot end is not heated to at least 150C.
    You can over ride this by sending a M302 to the printer.

  • Yes...when I had the hot end and motor separated I supported (for safety) and heated the hot end assembly well above 150 (step 6).  The motor does move (chatter) in that arrangement...just not continuously in one direction.  Thanks for the override advice, it may save my fingers.
  • check pin/connector area for blackened pins where motor plugs in. Could be poor connection.
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