A20 - all kinds of printing problems

[IT_Marco_93]

Hello everyone.

I'm really struggling, it's been some week now.
I am (was?) an happy owner of a Geeetech A20 printer.

I've finished my first PLA spool: it was an ICE white spool, and after some tinkering I had no problem with printing with it.

My GF bought for me a black PLA spool (I don't remember the make), and there was no way I could print with it... finally my nozzle got clogged and I had to completely change the extruder (maybe it was not necessary, but still)...

Anyways now I am using a SUNLU white PLA spool, which had great reviews on amazon. And there is no way I can get a good print... I'm experiencing underprinting, stringing and everything you can imagine... it also looks like the PLA sometimes randomly burns... As I said it's been some weeks now, I tried several printing speeds, travel speeds, fan speeds, bed and extruder temperatures, and every "suggestions" I could find on the internet.

I'm attaching several photos of a 0.1mm layer print, sliced with cura engine, where you can see random plastic pieces, the burnt surface (there is also a little stringing and some holes in the bottom surface)... I also attached a 0.4mm layer print, the original stl file and the gcode I used for the 0.1mm print...

Does anyone of you know why I'm having all these issues? Are there some tests I can perform to better understand problem?

Thanks a lot.