Unexpected retracts, any ideas?

[ketil]

Hi there,

I (still ) have an old M2, purchased in 2013, and it works pretty well but I'm seeing some issues. I'm hoping to get some input on a possible hypothesis that might explain what I've noticed recently.

I've been getting some uneven prints, and now I see something that looks like unexpected retracts during printing. I physically see the filament being pushed back out if the extruder, typically on direction changes. Here's a YouTube short showing what I see.

https://youtu.be/TwMTppGUgC8

Note that there are no retracts in the gcode as this is happening, neither firmware retract nor gcode rewinding the E value. So I'm guessing there's some physics going on..? But I find that surprising, even if it could be related to being too close to the bed and getting a pressure build up in the nozzle.

I'm using PrusaSlicer 2.9.1, and I based my settings on the MakerGear M2 profile that is included, with only minor modifications.

[airscapes]

Very first thing I would do is slice it on something else.. If you have an stl you can share I could slice it on the devil I know (s3d 4.01) and see what it does? Can then email you the gcode. if it is something small I can print it and see what it does on my M2. Or if something small mail me the gcode.. PM me you email if you want to exchange files.

[Gwhite]

If the machine is that old and has been used heavily, I would suspect an intermittent connection in the wiring harness. On the other hand, I don't know enough about stepper motor drive connections to see how it would reverse direction occasionally...

[jferguson]

I agree with GWhite. I found that the flexing of the cables connecting the heat sensor on the bed causes the copper strands to become brittle and ultimately break.

I bought a few marlin boards on the way to discovering what the problem really was.