See this piece:
That’s the heater cartridge that I burned out today. It turns out the heater will burn out if the temperature sensor isn’t well-connected thermally to allow the temperature to be controlled quickly. As best as I can figure my hotend is a mix of the new thermistor but not the latest heater block, which means there wasn’t a hole for plugging in the thermistor I got such that the end would be against metal. I didn’t realize the heater could be burned out if you’re not careful so I just inserted the thermistor in the through-hole on the far side of the block from the heater and stuffed some aluminum foil in the other end of the hole. That got me valid temperature readings, but they lagged the actual heater temperature by a bit too much: when I set the target temp to 300C to tighten the nozzle (so thermal contraction would form the seal between parts) the heater worked intermittently for a brief while and gave out.
I’ve since taken my dremel tool and embiggened (I’m sure it’s a word) the hole for the smaller thermistor so mine will fit, but I didn’t have a bit the exact right size so it’s a bit loose. I’m planning to essentially glue it in with thermal paste (which was suggested in the first place) before I tape it down. I also paid an absurd amount to have a new heater cartridge overnighted so I should have that Friday afternoon.
On the bright side, I can now upload firmware and the printer seems to be working properly mechanically. I was even able to extrude a small amount of plastic before I realized the heater wasn’t heating any more:
The fact that I could still push plastic through easily so long after the heater had apparently shut off is a pretty good indication that it well surpassed the 300C I had targeted.
The one thing I have left that I may be able to work on is the firmware: the lcd is attached and displays data, but I haven’t been able to access the menu I thought it offered (there’s a button and a knob for input). It’s entirely possible that there’s more to it than just turning on the “display” flag in the firmware so I’ll be looking for that tomorrow night.