Hello everyone,
I’d like to provide details about an issue we’re experiencing with the Teensy 4.1.
Main symptom:
The red LED on the Teensy blinks four times, then turns off, and repeats this pattern continuously. Additionally, the device is not recognized on the USB/COM port. No new connection appears when the Teensy is plugged in.
Recurring behavior:
This issue has occurred with other Teensy 4.1 boards as well, which had to be replaced.
Does anyone know what the four red LED blinks officially indicate? Is there a reference sheet or documentation we can consult for this? Any ideas on what might be causing it—crystal, flash memory, power supply issues, etc.?
Any help or suggestions would be greatly appreciated!
P.S.: Due to project specifications, the board is powered by an external source, so the pads that normally allow USB power have been cut.
Sometimes the teensy appears dead and doesn’t put up the USB port. Run teensy.exe. Open a hex file built for the teensy (arduino blink will work fine). Make sure Auto button is clicked (should be green). Make sure the teensy is connected via USB and powered up. Then, press the button on the teensy. The LED near the USB connector should blink bright for a second.
It should show in the Ports section of device manager now.
Also, it is possible to create a program that turns off interrupts and thus makes the teensy look dead. Use teensy.exe to force an innocuous program to be loaded.
Hi Gabrielle,
If you scroll down this page to the heading “4 Blinks = ARM JTAG & SWD Not Responding (Needs Crystal)”, you can see exactly what it means. I’ve been through most of these codes myself since I have made quite a few designs using Teensy.
So just to elaborate a bit - you’ll need an Oscilloscope to verify that the Crystal is oscillating. Compare signals with a board that is known good and try to see what’s different to that.