short circuit somewhere killing all my teensies?

As the title says, we are facing an issue where something keeps killing our teensy 4.1s. They are not able to run code that was uploaded, and they reach insanely high temps while running. In fact, we once misplaced a multimeter lead that had plastic insulation around it onto the chip and it melted though the whole plastic casing... That would have had to be over 150 degrees C for it to melt like that. We added heatsinks so we could keep one running long enough to diagnose the problem, but that was little use.

A few things we noted:

- Teensies would disappear from the list of devices in the Arduino 2.0 IDE.
- The program pin reads 0V in comparison to ground, and the button seems to have no effect.
- Button has no effect after some use, LED just no longer blinks after pressing and we are noticing no effect on the mode of the teensy after pressing.
- The 3.3V to ground reads 0.12V. From what I've read, this is indicative of a short circuit somewhere - but where exactly? We've checked all of our connections and new teensy 4.1s just die after half an hour of use.
- We made sure the VIN is max 3.3V.
- We have a regulated 3.3V going into teensy.
- Even if we keep the teensy plugged in, it just no longer uploads after a bit of the heat.
- Teensy experiences this phenomenon just plugged into the USB, but this only happens after we run it plugged into our main board.

We mount this teensy onto our main board as a sort of central brain. The main board is included below and exported from Fusion 360 Electronics and placed into a zip folder. JP9 and JP13 are 5V and 3.3V regulators respectively, JP 1, 2, 3, 4 are motor drivers from pololu, JP 15-19 is just some I/O leading to other boards. The diode array is just a color-sensing system for detecting white lines against a different colored background. VCC is 12V.

As far as I can tell, we don't have any short circuits, and we have no clue why this is happening. This also coincides with the fact that our motor drivers don't work, so that's another issue.

1712467950531.png
 

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- We made sure the VIN is max 3.3V.
- We have a regulated 3.3V going into teensy.
This sounds all sorts of wrong. VIN is meant to be 5V and it should be the only way the Teensy is powered - do not attempt to feed in 3.3v to the Teensy's 3.3v pins.

(The diagram you have attached is too blurry to be readable.)
 
This sounds all sorts of wrong. VIN is meant to be 5V and it should be the only way the Teensy is powered - do not attempt to feed in 3.3v to the Teensy's 3.3v pins.

(The diagram you have attached is too blurry to be readable.)
The schematic file is available in the zip folder.

We aren’t feeding 3.3V into the 3.3V pins, and when we tried to put 5V into VIN it just doesn’t work at all. We made sure the 5V supply is good. (It’s regulated).
 
Not a hardware guy, but are you powering stuff via the Teensy?
No, all the teensy is doing is just sending an analog signal (pwm) to some motor drivers for speed and a digital signal (logic low and high) for direction. It’s also accepting some 3.3V analog signals from a few photodiodes. There is no power the teensy is providing and all power goes through a 3.3V regulator and 5V regulator.
 
The schematic file is available in the zip folder.
Viewable with a third-party program... not exactly web-friendly.

We aren’t feeding 3.3V into the 3.3V pins, and when we tried to put 5V into VIN it just doesn’t work at all. We made sure the 5V supply is good. (It’s regulated).
Then something is wrong. Every Teensy 4.x ships with a card that labels VIN as "3.6 to 5.5 Volts". The main voltage regulator is probably underpowering the IMXRT, causing reverse current flow from the IO pins.
 
Viewable with a third-party program... not exactly web-friendly.


Then something is wrong. Every Teensy 4.x ships with a card that labels VIN as "3.6 to 5.5 Volts". The main voltage regulator is probably underpowering the IMXRT, causing reverse current flow from the IO pins.
Sorry man, the best I can do since the jpg just looks blurry.

I can try to look into this, but we tried and the teensy just would not work at all with 5V on the VIN.

I am confused on why the IO pins would backflow though, since they are all logic level signals and take almost no current, just a reference voltage.
 
Sorry man, the best I can do since the jpg just looks blurry.
In Eagle, you can
[1] "Print to File (PDF)" which looks very readable, or
[2] File > Export > Image. Choose resolution '300dpi' and it will output a very readable PNG image.
Your design seems to be done in Eagle 9.7 which I can not open in Eagle 9.6.2...

Paul
 
In Eagle, you can
[1] "Print to File (PDF)" which looks very readable, or
[2] File > Export > Image. Choose resolution '300dpi' and it will output a very readable PNG image.
Your design seems to be done in Eagle 9.7 which I can not open in Eagle 9.6.2...

Paul
Hi Paul,
The schematic was designed in Fusion 360 Electronics, so there seems to no option to export as an image.

I did manage to print it to a pdf file.

Please take a look and let me know if you see anything wrong.
Thanks
 

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As already stated, you should only put 5V (3.6-5.5V) into the VIN pin. 3.3V is simply too low for it to function correctly.

You show a possible connection to the VUSB pin. What is that connecting to if anything?

Also make sure that none of your connections on the Teensy are driving more than 3.3V back into the Teensy. You have I/O connectors that have 5V power to them.
 
As already stated, you should only put 5V (3.6-5.5V) into the VIN pin. 3.3V is simply too low for it to function correctly.

You show a possible connection to the VUSB pin. What is that connecting to if anything?

Also make sure that none of your connections on the Teensy are driving more than 3.3V back into the Teensy. You have I/O connectors that have 5V power to them.
We aren't actually connecting them, they just showed up like that on the schematic. We are only using the two rows of pins on the long side of the teensy.

We tried with 5V and it never worked.

Which I/O connectors have 5V power on them and are connected to the teensy?
 
Can't really tell from the partial schematics, but for instance you have a MUXBREAKOUT block with the only power pin being 5V that apparently has analog signals coming back to the Teensy on a different connection. Do you know if these are limited to 3.3V max?

In any case, the Teensy should run from 5V and not get very hot like you are seeing. Too high of voltage on an input pin will usually just damage that pin, so I would focus on a more serious problem with your baseboard. If it was me, I'd do the following:

1. Unplug the Teensy and all I/O from the baseboard.

2. Connect VIN of Teensy socket to 5V as it should be and with power off, measure resistance from VIN and 3.3V pins to ground and each other to see if you have any major power shorts. Would also check each pin on the socket to ground to make sure there are no other shorts to ground.

3. Apply power and verify that the VIN socket shows a good 5V between it and the Teensy ground sockets. There should be no voltage on the 3.3V sockets with the Teensy removed. I would then check for voltage on any of the other Teensy socket pins. From the schematic, it looks like there probably shouldn't be any with the I/O disconnected and Teensy removed.

4. Turn off power and plug a good Teensy in and apply power with a finger on the Teensy to see if it is getting hot. If it gets hot, shut power off and take a closer look at the baseboard. Maybe try powering from a current limited power supply to reduce chance of damage while troubleshooting.

5. If it doesn't get hot, start connecting the I/O cables one at a time to see if you can narrow the issue down to one I/O connection.
 
I don't understand your schematic. It shows many connectors, but no idea of what's really connected to them.

I see 17 LEDs (D1 to F16 and also D41) and 16 more mysterious 6 pin parts (Y1 to Y16) inside a box labeled "DIODES". But as nearly as I can tell (these sorts of schematics where almost all connections are by net names rather than draw wires are hard to follow) nothing in the "DIODES" section connects to Teensy at all. Those 16 mystery parts (Y1 to Y16) don't seem to connect to anything other than power and each other. Maybe I'm missing some important detail?

Also mysterious are the many net name labels on Teensy 4.1. Some of them, like "OUT1B" don't seem to exist anywhere else on your schematic.

I hope you can understand how useless this sort of schematic is for help you troubleshoot a problem. It gives us almost nothing to understand how you're really connecting and using Teensy 4.1.
 
I don't understand your schematic. It shows many connectors, but no idea of what's really connected to them.

I see 17 LEDs (D1 to F16 and also D41) and 16 more mysterious 6 pin parts (Y1 to Y16) inside a box labeled "DIODES". But as nearly as I can tell (these sorts of schematics where almost all connections are by net names rather than draw wires are hard to follow) nothing in the "DIODES" section connects to Teensy at all. Those 16 mystery parts (Y1 to Y16) don't seem to connect to anything other than power and each other. Maybe I'm missing some important detail?

Also mysterious are the many net name labels on Teensy 4.1. Some of them, like "OUT1B" don't seem to exist anywhere else on your schematic.

I hope you can understand how useless this sort of schematic is for help you troubleshoot a problem. It gives us almost nothing to understand how you're really connecting and using Teensy 4.1.
The entire box labelled DIODES isn't actually connected to our testing rig. But for future reference, I will reduce the voltage going into it to 3.3V when we do connect it. The Y pins are all LEDs and the S pins are all photodiodes. In our testing rig that we had this problem with, everything except for the MUXBREAKOUT box and the DIODES box was put together. The MOTOR_DRIVERS are for the pololu ones. JP 9 and JP 13 are these pololu regulators, respectively for 5V and 3.3V. MISC IO pins are just for extra 3.3V and 5V regulated power, in case we need them for something else or just general testing purposes.

The net name labels are the same as the pin names in the footprint. I have no clue why it's like that, but the teensy 4.1 footprints I found online just have those pins. I just proceeded with the pin numbers and referenced them to the 4.1 pinout diagram online and used it that way instead. In this case, OUT1B isn't actually used by anything else.
 
Can't really tell from the partial schematics, but for instance you have a MUXBREAKOUT block with the only power pin being 5V that apparently has analog signals coming back to the Teensy on a different connection. Do you know if these are limited to 3.3V max?

In any case, the Teensy should run from 5V and not get very hot like you are seeing. Too high of voltage on an input pin will usually just damage that pin, so I would focus on a more serious problem with your baseboard. If it was me, I'd do the following:

1. Unplug the Teensy and all I/O from the baseboard.

2. Connect VIN of Teensy socket to 5V as it should be and with power off, measure resistance from VIN and 3.3V pins to ground and each other to see if you have any major power shorts. Would also check each pin on the socket to ground to make sure there are no other shorts to ground.

3. Apply power and verify that the VIN socket shows a good 5V between it and the Teensy ground sockets. There should be no voltage on the 3.3V sockets with the Teensy removed. I would then check for voltage on any of the other Teensy socket pins. From the schematic, it looks like there probably shouldn't be any with the I/O disconnected and Teensy removed.

4. Turn off power and plug a good Teensy in and apply power with a finger on the Teensy to see if it is getting hot. If it gets hot, shut power off and take a closer look at the baseboard. Maybe try powering from a current limited power supply to reduce chance of damage while troubleshooting.

5. If it doesn't get hot, start connecting the I/O cables one at a time to see if you can narrow the issue down to one I/O connection.
You're right for pointing that out. They indeed are 5V signals coming back, but we never had the MUXBREAKOUT PCB actually attached during our testing, so that can't be the issue.

The Teensy we tried gets hot from even the USB connection when it's plugged into a laptop, and unnaturally so. We noticed this with all of them, and they do get hot from 5V.

I will try the recommended steps and get back with some more info.

We did try the 3.3V pin to ground as suggested in other posts about problems like these, but we got a reading of 0.12V. This hovers between what was described as a short in metallic connections and a short in the main processor from what I've read, so I have no clue what to make of that. Did we just get a bad batch of Teensies? We did order them together.
 
Hi,
Are you using overclocking ??? It is the only way to fry a Teensy when only connection is USB.

And when using motor driver, There is a risk to inject inertia energy in the power supply when braking. The power supply voltage raise, and could fry your 5V regulator.

What is your software ?

Angelo
 
Hi,
Are you using overclocking ??? It is the only way to fry a Teensy when only connection is USB.

And when using motor driver, There is a risk to inject inertia energy in the power supply when braking. The power supply voltage raise, and could fry your 5V regulator.

What is your software ?

Angelo
Just using Arduino 2.0 with the Teensy stuff installed.

No overclock, just 600mhz.
 
What do you call "hot" ????
If you run some simple software, like blinky or hello world, can you keep your finger on the CPU ???
The scale is something like:
1) Barely over room temperature,
2) lightly hot and no problem to keep your finger on the CPU
3) hot but your finger can still stand the temperature
4) very hot and you want to remove your finger after few minutes
5) Ultra hot and it is painfull keeping you finger on the CPU
6) Too hot, your finger is instantly burned.


Angelo
 
What do you call "hot" ????
In his first paragraph he mentions melting plastic on the CPU, so probably safe to say "WAY TOO HOT".

Seems like some kind of basic incorrect power issue to me. If you are using a footprint you found on-line, make sure that the pinout is correct. Your schematic shows both a VIN and 5V pin, but the Teensy only has a VIN pin, so makes me wonder if you might have a bad footprint with incorrect power or other connections to the Teensy. Can you export a CAD drawing of the PCB to PDF or .PNG?
 
In his first paragraph he mentions melting plastic on the CPU, so probably safe to say "WAY TOO HOT".

Seems like some kind of basic incorrect power issue to me. If you are using a footprint you found on-line, make sure that the pinout is correct. Your schematic shows both a VIN and 5V pin, but the Teensy only has a VIN pin, so makes me wonder if you might have a bad footprint with incorrect power or other connections to the Teensy. Can you export a CAD drawing of the PCB to PDF or .PNG?
It is a 4 layer board, but the middle layers are just 12V plane and GND plane.

I don't know if you can tell from this though, it is kind of difficult to see the bottom traces.

Edit: I exported another version with the bottom traces.
 

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What do you call "hot" ????
If you run some simple software, like blinky or hello world, can you keep your finger on the CPU ???
The scale is something like:
1) Barely over room temperature,
2) lightly hot and no problem to keep your finger on the CPU
3) hot but your finger can still stand the temperature
4) very hot and you want to remove your finger after few minutes
5) Ultra hot and it is painfull keeping you finger on the CPU
6) Too hot, your finger is instantly burned.


Angelo
I don't even need to run software, I can just connect it to the supply or my computer and feel my finger burn after about 1 minute left connected. It's hot enough to blister my skin and when we kept it running for longer it just started smoking.
 
The X's like you see inside the symbols below typically denote a DRC error that needs to be corrected before fab.

All SMD devices on the bottom side have these X's. Is there any chance that you flood filled the 12V plane on the bottom layer rather than one of the inner layers? That would short the 12V and 5V together amongst other things..

1712681389606.png
 
The X's like you see inside the symbols below typically denote a DRC error that needs to be corrected before fab.

All SMD devices on the bottom side have these X's. Is there any chance that you flood filled the 12V plane on the bottom layer rather than one of the inner layers? That would short the 12V and 5V together amongst other things..

View attachment 33979
This isn't the main issue and we are aware of these problems. On our testing rig none of the bottom SMD devices were put on.

Also, the bottom layer is not flood filled with 12V, when I select single layer view all I see are blue traces indicating the bottom layer.

I made sure the inner layer was the one that was a 12V plane.
 
Reviewing the board files and the schematic, I think the power supply to the Teensy is fundamentally not correct.
In the schematic, the Vin pin is labeled "+3.3V". That 3V3 comes from a regulator mounted on JP13.
3V3 is too low to power the Teensy. That's perhaps why Teensy's 3V3 regulator output shows 0.12V?
And as @jmarsh stated above: "VIN is meant to be 5V and it should be the only way the Teensy is powered - do not attempt to feed in 3.3v to the Teensy's 3.3v pins". As far as I can tell from the schematic and board files, you don't use the Teensy 3V3 output.

Is it possible for you to remove the regulator from JP13 and then power the Teensy over USB only?

Perhaps superfluous but if you power the Teensy over USB, you will see the USB voltage on the Vin pin as well as on the VUSB pin.

1712687894392.png


Paul
 
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