I just wanted to share an issue we had recently with a Teensy 3.5 based system. Our product controls some small industrial processes.

The on-site engineer reported complete failure of the unit which looked like a CPU hang up (display frozen, no Teensy LED flashing each second which we also use to know if the application is running). On power cycle the system worked for about 2-5 mins before freezing again.

Anyway, after an expensive swap out and carriage back to the workshop, I discovered that the SD card was very hot shortly after power up.

Long story short (no pun intended), the SD card had been slightly fractured and by chance was shorting out the supply rail. This was then causing the on-board regulator and/or the main 5V PSU to fail safe and shutdown (display runs off 12v, so was still on but frozen).

As you know, the SD card hangs over the edge of the board and indeed I have snapped a few over the development cycle. We therefore changed the board design to place a plastic cover over the Teensy and the SD card area (with a hole for the LED) to protect the card.

Perhaps this might be a useful lesson learnt for others.

Best regards