Dan,
I have a Monoprice Select Mini 3D printer that was printing great for the last 5 years. Then I decided to “upgrade” it with a new bed, “silent” control board, and a SwissMicro all metal heat brake. It hasn’t printed well since!! I got jams in the extruder constantly. I was never able to complete the Teaching Tech calibration test as the extruder would plug all the time
I went back to the original bed as I just could seem to get the new one to level. It helped a little. Still no good, though I could now level the bed.
I put the old heat brake back in too. Still had jamming. I practically threw it across the room, but I knew it was doing well before I started the upgrades.
It’s been sitting on the shelf for the last 6 weeks as I have tried to get my MP3D V2 working. (Another saga that has cost me almost two weeks of frustration. I took it apart so I wouldn’t sink any more time into it. I cut up the frame and threw away the printed parts).
I now think that the cooling fan setting(s) for the new controller board on the Mini is not running high enough to keep the filament from melting too early. Or perhaps the thermistor is not actually reporting the correct temp. I’m going to put the original controller back in and run a few more tests, but not until I get my glider flying for the season.
I chewed up WAAAAAY too much time screwing with the printers to just make a few simple parts for the glider. I bought a used Ender3 and have gotten some good prints out of it already.
So, Your problem may be due to the section of the extruder, just prior to the actual heating element, not staying cool enough. That’s the cause I read about in a bunch of online forums. I even printed a piece to install a larger fan on the Mini but I haven’t worked on it yet.
My real addiction is soaring (gliding) and I need a fix before I can go back to the 3D troubleshooting.
Good luck with yours,
Mike B.