Teensy 4.1's down - bricked?

viaxinel

Member
I am using the Teensy 4.1 with Dirtywave M8 Headless. Just a Teensy 4.1, a USB cable, and a 64GB MicroSD card.

Everything was working fine. I placed the Teensy in a plastic case designed for a laptop RAM chip. It is not airtight and has not gotten hot.

All of a sudden, the Teensy does not "boot" when I plug in USB. It is NOT detected by the loader. I've tried different USB cables that work with an external SSD drive. I've tried on Windows, Linux, and OS/X.

I have a multi-tester, but am not a "builder". I'm looking for ways to troubleshoot the Teensy. To put it into a loading state, to validate that it is not "bricked" and bring it back to life.

Any assistance would be appreciated. I can do a video conference if that would be easier to troubleshoot.

I have worked in IT infrastructure for 30 years so I know my way around computers - built hundreds of servers, so I'm pretty careful with static, but I can't for the life of me understand why this is happening.
 
Plugging in the T_4.1 does any part seem overly hot?

Posted this for 3.6 on another thread - only diff is the T_4.1 has a RED LED FLASH at the point the button should be released:

Code:
T_3.6 also has the 15 sec Restore feature that might recover to a usable Factory Blink if all is well.

Also, ideally with nothing connected ... press button and apply power, while watching a stopwatch. Release button at 15 seconds ( window is around 13-17 seconds ) and Teensy should then restore the MCU to factory state including a simple blink with no USB.

It should then go to a 1 sec blink - won't hurt to try a couple times if it doesn't seem to work.
 
Do you have a voltmeter? After pressing the button fails to help, the first thing to check is the voltage on the 3.3V power line. That can at least help to focus on whether the problem is likely power related / hardware damage versus something likely to be software / communication issues.
 
Do you have a voltmeter? After pressing the button fails to help, the first thing to check is the voltage on the 3.3V power line. That can at least help to focus on whether the problem is likely power related / hardware damage versus something likely to be software / communication issues.

I do have a voltmeter.

Both 3.3V read 0.00
The Vin reads 5V
 
Thank you,

I cannot detect any heat from the T_4.

I've tried the 15s reset which results in nothing changing.

There are NEVER any lights on the device - red, blue, solid, blinking - nothing.

See my comment below about voltage on the 3.3V Pins.
 
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Now we know it's power related, since you're see 0 volts on the 3.3V power lines. So there's no point messing with the pushbutton or LEDs. They're not going to do anything with the 3.3V power.

The next question to investigate is whether the voltage regulator (U4 on the schematic) is turning on and you get no voltage because something is shorting 3.3V to GND. This one is easy to tell, because U4 will get very hot. Usually the 5V power drops slightly, unless your USB power is very good and you have an unusually high quality USB cable.

If the regulator isn't turning on, the next question is whether the power management is intentionally keeping it off. This happens if you're held the On/Off signal low for about 5 seconds. But it can only stay off if the power management circuitry has voltage, like from a coin cell on VBAT. Without any power, the board should always boot up fresh and try to turn on the regulator.

From there (assuming the power isn't intentionally off), to *really* start digging you need to look at the power up sequence which is documented on this page. Look for the schematic with buttons that highlight the wires for each step.

https://www.pjrc.com/store/ic_mkl02_t4.html

For example, step 2 describes USB_CAP and SNVS_IN. You can find those on the schematic. On the Teensy 4.1 page you can find a map of where each component is located, which can give you the places to (very carefully) measure voltages to check if each step is happening.

I have no way from only the info so far to know what's wrong, but if you want to dive into checking, hopefully this gives you a clear path forward to discovering where the problem may be.
 
Thank you so very much for that description and guidance.

I have followed the boot process and used the Test Points on the "back" of the device.
PMIC_ON_REQ: 1.2/1.3 mV
AD_B0_00: ~15mV
VDD_SNVS_IN: 0.1mV
PTA0: ~45mV
PTA2: ~45mV

There is no heat on U4 whatsoever.

I really don't see how I could have damaged anything - it was just sitting in this plastic case:
https://photos.app.goo.gl/LEee2XYNN7PfAX688
 
VDD_SNVS_IN: 0.1mV

Ok, this definitely means your board isn't powering up.

As you can see in step #2 of the powerup sequence, VDD_USB_CAP is supposed to reach about 2.5V when power arrives at USB1_VBUS and USB2_VBUS.

So more questions / measurements....

Are you getting 5V on 2 of the 3 pins on Q1? That would confirm 5V is getting to USB1_VBUS & USB2_VBUS. If no 5V here, look for damage to F1, L2, Q1.

Are you seeing 2.5V on C17 & C31. That would check whether the USB regulator inside the chip is creating VDD_USB_CAP at 2.5V from the 5V input. If no 2.5V here, look for damage around C31 area, maybe something shorting to GND?

If you get 2.5V for VDD_USB_CAP, then check D1 for damage, since it's the only part between VDD_USB_CAP and VDD_SNVS_IN, which you've measured as basically zero (should be 2 to 3 volts).
 
Only ~50mV at the top (single) pin on Q1 - towards the middle of the board.
5V at F1 - both sides

No apparent damage.

No Voltage on C17 or C31
No Voltage at VDD_USB_CAP (first thing that I checked) or damage to D1

No hairs or shards of metal

I've got 2 boards with the exact same problem.
 
There is no surface-mount at L2 on either of these boards.

On one of them, there is nothing on C28, or C7 either.

Is it possible that I've got a couple boards with questionable surface-mount components? Are there knock-offs?

On one board, the C27 is labeled C6 and another, it is labeled A4.

https://photos.app.goo.gl/zjSi4qFo1vNA54RU6
 
This is the L2 location on the bottom side.

l2.png
 
So I've got missing surface-mount components missing.

I guess that when the boards warmed up from use, some weak solder joints and mild G-forces could have caused them to come loose.
 
Looking at the photos. Didn't see the link a moment ago. You can post photos directly here on the forum by clicking "insert image" in the toolbar.

Indeed it seems these 2 boards have been damaged, where parts that should be on the bottom side appear to have been broken off. They look like genuine Teensy 4.1 which have been damaged.

If you want to attempt repair, try the one which is missing only L2. Just solder a piece of wire between the pads. L2 is only to help keep high frequency noise from escaping back up the USB cable. The board should work fine without it.
 
Also, the "C6" mark is not identification of a capacitor. On the other board it is "A4". These boards are made on a panel, where this mark identifies which location the board was within the panel during manufacturing.

They are made with lead free solder which should not melt below about 200°C. I can't know how these came off, but if high temperature was involved, it would have been very hot.
 
Difficult to say. They definitely could not pass testing without L2. So if they work when L2 is replaced by a wire (have the bootloader in the MKL02 chip) they must have passed testing. Two tests are performed, where the bootloader is written during a first bed-of-nails test, and the LED blink program is written during a 2nd test where the operator plugs in a USB cable and presses the button. Neither test can pass without L2. But the test process can't mechanically check the strength of soldering on the parts, only that the electronics works during the test.

Here's a copy of the image and the bottom side photo from the product page for reference. If anyone else experiences this L2 missing product, hopefully these pictures will take the mystery out of the problem, and this thread can serve as a place where we find out if other people are having L2 issues.

l2_missing.jpg
 
Hi, folks.

I need an opinion that I think is relevant to this thread.

I just started with my Teensy 4.1 today and was working through the tutorial (I'm a software guy, not a hardware guy.) After getting the basic blink program working, I put the Teensy in a bread board and wired up an RGB LED. When I applied power to the Teensy the LED on the board didn't start to blink, and Teensyduino can't see the board.

Evaluating with a multimeter shows me that the 5V pin is live, but both 3.3V pins are registering 0. I'm guessing putting it in the breadboard caused something to break (how much force should it take to put something in the breadboard?)

Practically speaking, is there anything I could reasonably do to revive this board? I can try to diagnose this problem, but even if I figure it out, is there any way for me to fix it?
 
First, visually inspect the bottom side of the circuit board. If L1 is intact, you probably have a different problem. That's fine, just start a new thread. I and others can try to help you troubleshoot, like what happened on this thread. If L1 is also missing, please try to take a close-up photo.
 
I created a solder bridge across the terminals where L2 used to be located. This revived my Teensy 4.1 and I have been successfully using M8 Headless ever since!

Thank you!

Looking at the photos. Didn't see the link a moment ago. You can post photos directly here on the forum by clicking "insert image" in the toolbar.

Indeed it seems these 2 boards have been damaged, where parts that should be on the bottom side appear to have been broken off. They look like genuine Teensy 4.1 which have been damaged.

If you want to attempt repair, try the one which is missing only L2. Just solder a piece of wire between the pads. L2 is only to help keep high frequency noise from escaping back up the USB cable. The board should work fine without it.
 
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