I would add this to the instructions as well, but Hackaday.io is a bit special in that it wants me to edit ALL instructions at the same time.

Someone made a mistake on the driver board V3.01 (it was me). The pullup for the nozzle check signal is pulled to 12V, not 3.3V. This means that an input for the Teensy is being pulled to 12V most of the time. I myself have not experienced any issues whatsoever with this, but I suspect some other people I have been talking to have experienced issues (broken Teensy's).

I am working right now on a V3.02 design that will pull the check to the right voltage. I advise anyone who want to make this not to use the V3.01 driver.

However this new design will not fix the problem for people who already have a board. Below is a fix for this issue. TL;DR is tombstone the resistor and solder a wire to the nearest 3.3V.

The culprit is R8 (shown here as P8, because the silkscreen is worn off). Desolder it.

You are now left with 2 pads. The pad closest to the R8 silkscreen is the check pin. The pad furthest away from R8 silkscreen is 12V. Solder one side of the resistor you desoldered (or another 10k resistor) with one side to the check pin, facing up (tombstoning it).

Now a wire needs to be soldered from a 3.3V pin to the side of the 10k resistor facing up. R11 and R12 have 3.3V on the pads closest to the silkscreen. First solder a wire to the R11 or R12, then bend the wire to R8 and solder it to the side of the resistor facing up.

Now the check pin is pulled to 3.3V and the check pin is no longer capable of destroying the Teensy.

(Edit 20 minutes later: While designing V3.02 I found an even bigger mistake in the PCB on the TLC driver. It shorts 12V to ground, and several signals directly to ground. It is not in the Gerber files (V3.01 still had V3.00gerber files in it) but it is in all versions of the KiCAD files. The TLC driver has moved 2mm to the side and shorted on everything. I will fix and upload ASAP because this is a real problem. I have no clue how this one got in, but it is quite a bad one. My apologies)