Strange banding on first layer/skin I've been printing for a while with a Creality CR-10S with Colorfabb black PETG economy and all was good.
Until today, where on a large, flat print (30x10cm - a small drawer) I can't manage to get a smooth first (or second) layer no matter how hard I try.
I tried so far:


calibrating the extruder
setting different temperatures (range 230-240 suggested by the manufacture is 235-250)
slowing down the print (I usually print skin at 80mm/s, I tried this one down to 40mm/s)
installing a brand new nozzle
levelling the bed


The print starts fine but then, randomly, some bands that look like under extrusion appear:


Here's a second example of the first layer - I've ripped it off the plate but as you can see the first 50% of it was fine. The problem appeared later in the process.


The extruder "clicks", the filament stalls and it's clear that the nozzle is not extruding plastic fast enough.
What can it be?

All other prints are fine, but I have to say this is the only one that has such a large horizontal surface.
i'd say your extruder driver and/or motor is overheated - really 

according to your description - when you've printed other things it was fine but this is the first with such big "flat" area

usually extruder motor works for some time then stops and starts and so on and again so it has some time when driver cools down but here it runs constantly for relatively long time

this overheats the driver and/or motor then is starts to clicks as there is not enough current delivered to the motor

what can you do?


try to take the cover off
check the driver temperature (use electronic thermometer as it can be even 100C)
try to cool it with some kind of fan while running the same printout


if the diagnosis is fine - you are at home and now you know what to do ;)



the one described as E is the one to check and cool down