Over Thanksgiving/National Day of Mourning, I upgraded my Prusa Mk4 to the Mk4S. When I went to initiate the self-test, it failed. I hadn't run the test in a while so likely it had been out of whack for a bit, but it threw me off. The nature of ADHD is such that small things can throw off a whole multi-step process, and then months go by in a blink.

Fast forward to a few days ago, I finally finished tearing down and re-assembling the Y-axis. Boom, test passed!

But wait, what's this? The heater test is failing? It seems I damaged the thermistor wiring in the hotend at some point in the upgrade. I ordered a couple from Prusa and waited.

With the new thermistor in hand, I tried to replace it, only to find that plastic had gotten into the tiny screws in the hotend (I had some very messy spaghetti prints early in the process). The tip of my T6 Torx screwdriver snapped off in the set screw, leaving me unable to remove the thermistor or heater. Next I ordered some replacement heat blocks.

Finally, last night I put a new heater element, thermistor, and nozzle into a new heat block and fired the self-test up, at last! Success 🎉

However, the thermistor, heater, and heat block are all currently 3rd party parts and their tolerances aren't at the same level as Prusa—there are wiggles where there should not be wiggles. I'm waiting for OEM parts and will swap them all out when I can, but for now I'm doing some calibration and test prints. It's been a few months and I have a major backlog, but it's best to make sure things are working right before proceeding.

Next I'll install the MMU3 upgrade from Prusa, and multi-material printing will be within reach. I'm thinking about the Core One upgrade as well, but that's another $400 at early bird pricing. With recent news I'm very glad not to be in the Bambu ecosystem, but damn, it's still expensive (and filament only likely to get moreso with tariffs).