Geeetech

z-wobbling : I had similar issues. The minimal bending of the threaded road and maybe a collision to the upper fan of the extruder is the issue. Just to be clear the Z-Coupler must be assembled in the way it can compensate misalignment. Does mean the threaded rod mustn't touch the Motor- Z-axis. 5mm horizontal distance must be default.

Additionally you have to be careful with the fixture of the road. Also here you can create worst case 0.3mm misalignment (or compensate )

ball bearings : Please check my assembly suggestion for the Y-axis ball bearing. Some additional washer ad a distance part really helps. I ruined my first bearing also and was wondering of Y-axis wobbling and missalignment...

A4988 drivers : The X-axis worked fine for me. Same for the Y-axis until I killed my bearings on the other side. Took me days to find you where the extra enormous forces would come from. Please check also your X-bearings. Maybe same problem.

X axis endstop : Agree. Thex changed the end-stops and now everything is 3mm to far away. Have problems with x,y, and Z and helped myself by some modifications.

firmware : Same issues (all of them). Really crap and the bad thing there is no source code to fix it. This is really pain in the ass.

Firmware 1.0.4 installed
No visible improvements : still the same communication issues (each line needs to be resent), no access to SD Card from Octoprint...

@elocm

I almost completely solved the z-wobbling issue by replacing the metal couplers with printed ones (https://www.thingiverse.com/thing:1264447). The threaded rods are a bit bent but the main problem was the poor quality of the metal couplers (8mm and 5mm holes were misaligned).

I replaced all the ball bearings (X & Y axis) with new ones and it works perfectly now. Moreover, filling-up the LM8LUU with lithium grease dramatically reduced their noise.
I also ordered a second heater cartridge for the hot end as it has difficulties to reach and maintain the temperature needed for ABS (cannot go above 235~240°).

Regarding the firmware, I ordered a RAMPS board and I will try to use it on the M201 with dual-extruder capable firmware.

Finally, I am printing parts for building a delta printer (Kossel mini) and a MP CNC

Same error on my side on big prints

As soon as the gcode exceeds 1M of line, I'm still getting the same error in loop:
Error:Line Number is not Last Line Number+1, Last Line : 1000001

Can you please give us feedback on this issue ?

which is the correct voltage for A4988 Z axis?

0.8v-1.2v is appropriate. And you can refer to this post.
http://www.geeetech.com/forum/viewtopic ... 17&t=17038