M201 - problem with Z axis

[CICOtheMajstor]

I purchase two weeks ago Geeetech Prusa I3 M201 printer .
Unfortunatly till now i do not solve problem with Z axis . When axex move up or down they stall , motors humming and then after few second moves .
Do they booth motors (42SHD0034-20B) have only one step driver A4988 ? Can I adjust a Vref (on what value) that motors have more power ? Which driver on board GTM32pro is responsible for this ?
Or maybe is solution to by strongers motors (what kind or type) ?
In the proces of build this prunter I allready need to make a little bigger holes on booth Z-top mount because without this the lead screw can not turn with hands .
I have mechanical knowlege and I check all parts many times but unfortunatly can not find real solution for this problem .
Can anybody give me a tips ?

[franktattoos]

UP !!!
I have the same problem here.

[bang]

This pic has a good illustration for the driver:

QQ截图20170316091519.jpg (39.55 KiB) Viewed 7533 times

As for Z axis issue,check this file to make some troubleshooting:

I3 Z axis.zip

(281.49 KiB) Downloaded 1167 times