I recently got a teensy 4.1 from sparkfun. It works sometime, but after a while (few minutes) it stop responding and the board gives me 9 blinks.
If I restart the board after that, I get 4 blinks which seem to point to “ARM JTAG & SWD Not Responding (Needs Crystal)”.
Measuring the signal at C1 (Teensy® 4.1), I do not see the 24 MHz signal when the board is in this state (when the board is in a working state, I clearly get the 24 MHz signal).
Is the Y1 crystal defective?
It sounds like it; I found your order and will get a replacement sent out ASAP
Hello TS-Russell, I recently purchased a Teensy 4.1 from SparkFun, and am experiencing the same issue(s). Initially, the board worked, but then went into 4-red-blink mode. There was once instance when it did 9-red-blinks, but it’s been consistently 4-red-blinks otherwise. I’d be happy to send it back, if a replacement is possible.
Was it purchased from us? If so head over to Return Policy - SparkFun Electronics (contact vendor if purchased elsewhere) and we’ll get ya squared away
@TS-Russell yes, it was through your website. Thank you for the link, I initiated a refund. Would you be interested in having the unit back, to investigate? I have since ordered and received another, which is installed in my project and working without any hiccups!
The CS rep will give any relevant instructions hereforth 
I’m seeing this too. Teensy 4.1 is part of a product we manufacture. One of the units was working and then suddenly bricked with a crystal failure - 4 flashes, no startup or response to button press. I hope Sparkfun will look into this. PJRC had incredible production quality and we need that to continue under Sparkfun - we can’t have our boards failing in the field.
Sorry to hear you got unlucky…though there are always going to be some amount of defects; even the Raspberry Pi stuff which gets fully QC-verified and tested at production show 0.5-2% failures. SparkFun sells “hobby-grade” products…if any risk of failure is catastrophic for your use you might need to look at “industrial” MCUs/products
We offer a 30-day no questions guarantee for situations where boards are deemed defective if that applies