Teensy4.1 no LED, no 3V :(

der Warst

New member
Hey there,
I have a Teensy 4.1 which was working fine. I was working on other projects for a while and now that I wanted to use it again, it doesn't seem to work any more. I tested it with a multimeter and there's no voltage on the 3V pin. 5V is there, so the USB connection seems to be fine. The fuse is fine, too. There's 5V on two pins of Q1, and nothing on the third. Am I correctly assuming there should be 3.3V on this pin? Is there anything I can do to save it, or is it gone? I'm kinda confused what could have happened, since I just had it connected to a computer 3-4 times, didn't solder anything to it and it was just lying on a shelf in the meantime. How fragile are they?
Thanks for any help.
 
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Am I correctly assuming there should be 3.3V on this pin?
Nope, the third pin is the gate of the FET connected to GND. See schematic.

T41.PNG

You may want to check whether the output of U4 [a TLV75733P voltage regulator] is shorted to GND somehow.

Paul
 
Nope, the third pin is the gate of the FET connected to GND.
Thanks for the clarification. I mistook it for being involved with the voltage regulation.

You may want to check whether the output of U4 [a TLV75733P voltage regulator] is shorted to GND somehow.
Done, no short.

Sooo, dunno. Should I get another TLV75733P and replace it or is it unlikely that this one is broken? I have no experience with teensy's so I'm not quite sure what to make of this. How likely is this part to fail? Especially since I didn't even really use it. In the documentation, it says that this part got replaced with later revisions, does that mean it was problematic to begin with?
 
If I read the datasheets correctly, both the TLV75733P and NCV8186 are short-circuit protected and therefor unlikely to fail.
If you don't see a short from 3V3 to GND, you could power the Teensy from 3V3 only [inject the power at the 3V3 pin] and see if it comes alive.
But read this first.

Paul
 
...
But read this first.

Paul

Good find on that post @PaulS.
Very few T_4.1's ever indicated here with any such problem as this post.

They catch my eye since I had two quit working in short order for no known reason. I didn't trust my hamhanded meddling, or find that post (then a year old) - I just mailed them off 'to the factory' with the cascading series of crises, perhaps they landed on a low priority someday shelf.
I have three active on my desk just now - and no trouble but those two since the many used from first of 4.1's Beta hardware.
 
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