USB on Teesny 4 stop working?

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donperryjm

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I have a teensy 4.0 that was working fine the day before. Connected today and i can get no usb connection. Tested another T4 and connects fine.
The problem teensy has a sketch on it that briefly blinks upon startup, so i suspect the mcu is doing OK. But no USB

This teensy has the powerline cut and was getting a regulated 5V power through to its 5v pin. Teensy wasn't tested on anything mechanical or anything, just some oscillioscope testing. But, USB is dead. Any thoughts?

Btw, this is the 2nd T4 to do this very thing.
 
The first question for a dead Teensy (or dead anything electronic) is whether it is managing to power up.

Teensy 4 has a complex power up sequence. It's explained on this page. 3.3V power turns on in the 6th of 8 steps, so just checking whether 3.3V power is present is a pretty good check.

If you do have 3.3V power, the next easy thing to try is pressing the button for 15 seconds to restore the default LED blink program which uses RawHID for USB communication.
 
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