I'm encountering an issue with my trusty Mk2 trying to print a largish bed-area model in PETG. I need a very clean first later, but I'm getting a poor bottom surface finish in the top left corner of the print. It looks like the filament isn't adhering consistently to the bed and is blobbing up. At first I thought it was a levelling/z-height issue, but after spending a while trying to dial it in I haven't had any success getting a better finish. Wondering if it might be a temperature thing, I tried out my thermal camera on the bed and found that the uniformity of the bed heating was pretty off (the bed temp was set at 90c and was holding at that on the info display):
Yikes! That's almost 17degC over target at the top left of the bed, and 3degC under in the centre. Most of the bed was around 3degC over.
I haven't had chance to experiment with lower temps for my print, but in the meantime I wanted to ask the community if this degree of variance is expected or if there are known faults/defects that might cause it (I've read about possible side-effects of bed damage that might affect the heating traces, but my bed is in good condition and hasn't got any obvious cracks or flaws)?
Any thoughts or ideas appreciated!