Teensy 4.0 seems dead.


I killed my board and it just gets hot around the USB port if plugged in, the LED does not flash any longer, and the IDE does not recognize it. I desoldered all of the wiring from it and cannot see any physical damage. I have another board that works and I can use as a replacement but I am curious how I did this. I don't want it to keep happening.

I am mainly concerned that I am somehow over drawing from the 3.3v pin or maybe back feeding power but not sure how. I am using a 12-24v to 5v Voltage reducer to power the teensy and an LCD screen. I am using 4x MAX31855 boards, 1x BPM280, and a rotary encoder as well that I was powering from the 3.3v pin on the teensy. From what I can tell I am below the max output of the pin but I would like to be sure. My device was working fine until I started to add in the rotary encoder function then after a few uses of it the board sort of froze, then began to get hot and unrecognized by my laptop. I desoldered everything and here I am.

I have also Run the additional hardware from the 5v output of the reducer successfully but changed the power wiring to the 3.3v pin when I noticed I was having inaccurate readings from my temp sensor after powering the reducer up. The problem di not occur when I used the USB as a power supply however. At first I thought maybe it was the way I had the sensors wired so I experimented with the 3.3v pin and changing my grounds around. It ended up being a noise issue with the switching power supply I was using to power the voltage reducer on the bench. I since started using a 12v power supply that came with an old router that I had stashed and that cleared up my inaccuracy issue, but I left the hardware wired to the 3.3v pin. This device will eventually be powered by a 12v battery/powersports charging system.

Can anyone think of something else i should be investigating here before I move forward? I am barely getting by with a lot of this stuff so I have been known to overlook details and make mistakes to say the least. I would really like this to not become a regular issue. It is possible I blobbed some solder but I have inspected it thoroughly and do not believe that to be the case.

I appreciate any help I can get in advance!
Quick voltage measurement on the 3.3V pin can usually confirm whether the hardware is still good and just needs something like the 15 sec button press versus actual damage. Of course the hardware can be damaged other ways. But if you see something like 0.3 to 0.9 volts on the 3.3V line, that's usually a sign a chip is damaged internally. If you see 0 volts or only a few mV, that's probably a sign metal somewhere is shorting the power to GND. Often those problems can be fixed if you're able to find and remove the stray solder or metal debris.
I checked and I get .033 volts. I will give a good look around for some debris the best I can.
Just as the last time I appreciate the fast response.
If you don't find it quickly, something you can do to get more information (which might help or might just be too much info) is measure mV between 2 GND or 2 power locations. If a large current is flowing through the traces / planes between those 2 points, you'll see mV measurements. If little or no current is flowing along that path, you'll see zero volts. Actually putting that knowledge to use isn't as easy as it might seem, but if you're completely stuck maybe extra info will help you move forward.