Teensy 3.6 get's hot and does not work anymore

[most]

Hi guys!
First of all a little disclaimer: I am by no means well educated in terms of electronics and programming etc. However during the last year I spent a lot of time building a camera robot. Therefore my knowledge is not even nearly as good as it should be when building such machines. Please be patient with my silly questions

I have a pretty strange problem with my Teensy 3.6. I use it to control my 3 axis camera slider. I use 3 NEMA 17 motors which are driven by TMC2130 and controlled via a Software called PureMoCo (https://www.puremoco.com/pages/firmware.php).
I designed and ordered myself a small little PCB to make the controller as compact as possible. It worked fine for pretty much half a year. However one day it just quit working and I am not able to track the problem down.
The teensy does not boot up properly and I am not able to connect it to my tablet via Bluetooth. The only strange things I noticed are:
On the Teensy there is a small little resistor near the USB port. It gets really hot after 5 seconds.
The LED on the teensy used to turned on solid whenever the slider was working. But after a few times using the slider it stopped working or blinked strangely. However it did not affect the usability of the slider. I guess But I thought it was worth mentioning.

I am not able to connect the teensy to a computer. I think it is dead... It also seems strange to me that the controller worked for half a year and out of nowhere its dead now. I checked all the connections of the PCB trails and there is no shortage. I could not find any damage on the board. The voltage supply is also correct. I cut the VIN Pads apart and used two diodes to properly power it. I have attached a pretty BASIC wiring diagram of my circuit as well as some pictures. https://www.dropbox.com/sh/chb3cwipc8fkac7/AAA5XvSvaXH2AmU3Yo9iqdpGa?dl=0 (I could not figure out how to attatch the pics to the thread. It always said "failed to upload" sorry!)

What could be the reason for my problem? Why does the resistor get so hot, even when powering it via USB? I have already bought a new Teensy yet I haven’t installed it since I don’t want to destroy another one

 

[GremlinWrangler]

The component getting hot is probably the poly fuse (top left corner https://www.pjrc.com/teensy/schematic.html )which means something is drawing excess current. Reasons for that are generally:

Something wired to the teensy is drawing to much/failed (sounds like you have tested with it unplugged so not that)
Something on an output went wrong and that output pin is dead in a way that produces a short
The Teensy got more than 3.3V in and shorted internally.

If you can, unplug the Teensy from the board and USB and wait for it to cool, compile 'blink' for T3.6, hold in the program button, plug in USB and release the button. This should prevent anything in your current code doing anything and prove if your teensy CPU is dead, or if the problem is more peripheral.

Another check is with Teensy plugged and on (insulating) bench measure resistance from all pins to Gnd and all pins to 3.3V

In terms of where the problem started options are:

Output to drivers got shorted in some way and damaged the output driver transistors, check the wiring for anything that might touch (or is still touching). Adding 100-500 ohm series resistors to outputs can make things more robust against this.

Drivers fed back spikes from the steppers - They should not do this but can happen if drivers are problematic, or in some cases if motors are moved mechanically with power off (generating power).

The power supply to the Teensy went above 5.5V and exceeded the onboard regulator limits, this can happen due to the stepper motors producing widely varying loads but your careful design with seperate 5V and 3.3V supplies should have prevented that as long as the 5V supply was good, maybe check what it outputs as the motors start and stop running.