After much fiddling with connections I was able to get the replacement QU-BD extruder wired up and ran a couple of extrusion tests.
The short version of the story is, it didn’t work.
The long version is that after several attempts, I was never able to get any material to appear at the end of the nozzle. The filament would feed briefly, then jam. After disassembling the extruder, the end of the filament looked like this:
It occurred to me that perhaps the extruder was tested with ABS instead of PLA (which is what I use) so I ran the temperature all the way up to an indicated 240C, but to no avail.
My last guess at what is wrong is that the indicated temperature is incorrect. I’m going to double-check the thermisistor tables in the firmware and I’m considering picking up an infrared thermometer to measure the actual nozzle temp (although I’m not sure reading the external temperature is useful).
I’m also planning to order a J-Head to get my old Makergear extruder ready to go again.