Z surface not smooth?

Z surface not smooth? Only happen on 1 M200 recently, what's wrong?

looks like clogged nozzle. I suggest you [url=http://support.zortrax.com/nozzle-cleaning-m200/]clean nozzle[/url], if that wont help - [url=http://support.zortrax.com/nozzle-replacement-m200/]replace[/url] it