New Teensy 4.1 bricked - U4 chip overheats with USB

Jay Converse

Active member
I've seen the other threads about this being a power short problem. This is not my first Teensy, I had some new code running fine: https://imgur.com/gallery/kZRfvxw/comment/2315634137. The only problem I was having was some flickering on the animation, but I figured I just needed to debug the code.

Suddenly it bricked, and I don't know why. It doesn't even register as a USB component any more. I can plug my old teensy 3.5 into the rig, and it's fine, so I don't think I shorted anything.


Where do I start to diagnose?

Regards,
Jay Converse
 
Have you tried resetting it to factory? Does the factory reset run and does that revive it?

Memory Wipe & LED Blink Restore

Teensy 4.1 will fully erase its non-volatile memory and return the flash memory to a simple LED blink program if the program button is held between 13 to 17 seconds. The red LED flashes briefly at the beginning of this time window. During flash erase, the red LED is on bright. When completed, Teensy 4.1 will automatically reboot and run the LED blink program, causing the orange LED to blink slowly.
 
Yep, I definitely did it before, and I just did it again, 3 times, 13, 17, and 60 seconds. As soon as I plug it back into the USB, that chip starts to cook. I guess I'll just order another one. Dang it!
 
Have you visually inspected the board under magnification to verify that the soldering looks good and no parts look cracked/burned? Read elsewhere where someone found a cracked cap (fortunately it was not critical) to the board. Maybe someone with more electronics/Teensy experience can recommend some "next steps".
 
First step to diagnose U4 overheating is measuring the 3.3V power.

If you see only millivolts, the short is probably metal. Often this sort of failure is fixable, if you can find and remove the stray metal.

But if you see something like 0.3 to 0.9 volts, that's usually a semiconductor short inside one of the chips. The main processor is the most likely. Those sorts of shorts inside the chips usually aren't feasible to fix.
 
Alas, I get .18 on the 3.3. She's dead, Jim. I wish I knew what I did, Teenys are very robust. Maybe I have carelessly brushed a hot 5V wire somewhere.
 
So anyway, while I wait for the new one, is there anything I can do to salvage something from my fancy new brick? I don't have an oscilloscope, just a multimeter, so all I can tell you is 3.3V is totally shorted to ground.
 
I think I have a conclusion to this sordid story.

I got my new 4.1, blink test was good. Plugged it into my rig, and poof, it's gone. WTF??? I'm not an EE but I'm smarter than this!!! So I check things, and s#$t!. The audio shield underneath was plugged in backwards. Dammit. I hate it when I break my toys.

New order placed. Hopefully you won't hear back.
 
Was a SD card in the socket? If so, it probably got hit with 5V on the MISO signal (Teensy pin 12). It probably gave a path for the 5V to hit other stuff that's not 5V tolerant.

Without a SD card, MISO normally wouldn't connect to anything.
 
LOL, that's exactly what happened. The last thing I did was plug in the SD card because it has lots of GIF animations on it, it's an important part of my rig.
 
Back
Top