I tried again with simpler STL files to try to debug the problem. The flow of material through the nozzle was irregular. I cleaned the nozzle but this led to no improvement at all.
Then I looked for failure in the extrusor stepper.
I readjusted the trimpot of the stepper driver, but the voltage and the amperage was set correctly. The stepper didn't miss steps, and, if I push material using the manual control from software, the correct amount is pushed through the extrusor.
The gear doesn't have any visible imperfections and the error is not triggered by any visible event (like every full spin of the motor, etc) Even if I try to push material manually, can't appreciate any jam or obstacle. Even I replaced the whole hot end piece with a brand new from Geeetech so I discard a problem with the extrusor...
To illustrate the failure, I've printed a big flat surface so the irregular flow is visible in the first layer. Of course, the bed is properly leveled.
I've tried different combination of temperature and materials and, before the said error, I've achieved successful prints with both ABS and PLA. Neither materials works now.
Thanks
