I'm so confused.

I started going thru some of the fixes suggested here. To start I was going to try disabling the retraction to see what happened. I could not get the filament to flow thru the nozzle even before the printing started. So I took everything apart again. Replaced the tube and fittings and nozzle - again. I checked the hot end - shone a light thru it - looks perfectly clean. I added a washer to the extruder to make sure there was enough pressure to push the filament. After that the filament flowed so easily, I wondered if maybe that section of tube had a defect or something that was affecting the flow? So I checked the tube and sure enough it felt like there was resistance when I pushed filament thru the disconnected tube.

So instead of the 0 retraction, I tried to print a known file from my sd card. This is what I got - a stringy, globby mess with uneven sides. To this point, it's functional and strong, but ugly. I stopped the print because of a glob on the top surface that the nozzle was bumping into - probably would not have finished. I have succesfully printed this same gcode twice before.

20201220_152452.jpg

So I took the washer off of the extruder in case that was somehow causing over extrusion. I didn't get past the first couple of layers on this try. Globs of melted filament all over the print. Again this is from g-code that successfully printed before.

20201220_163854.jpg

When I watch the extruder work, I don't see any slipping or skipping like before.

Keep in mind that the clogged section of tube was brand new and I had an under-extrusion problem before I installed it.

Trying to print from previously proven g-code proves that it is a mechanical issue with the printer, right? All the belts seem OK.

How can I tell if the thermistor is bad. there is a spot on the end of the glass ball, but it looks intact.

Any ideas what else I can check? Thanks

Donna