New 4.1 Out Of Package No USB Communication


I've purchased many Teensys in the past, never a problem ( Great product ) , until today.

4.1 ( New out of package ) is not recognized by USB.

Here is what I have...

Good 5.0 Volt
Good 3.3 Volt

When I plug the usb cable into the 4.1, nothing happens...

No Beep-Beep, Nothing

Pressing Button Does Nothing.

Holding button for 30 seconds, then waiting 2 minutes, nothing.

Tried external 5.0V supply , nothing.

No Port Seen In Teensy duino.

Tried Plugging In A Different Teensy 4.1, All Good, so cable is OK

Only activity on Teensy Board I see....

Tiny ( really tiny ) LED Just Below The USB Connector blinks once every 34 seconds.

Tried uploading example blink program, but pointless since no communication exists.



Thanks For The reply & the link.

I will try that & let you know the results.

Thanks Again

Well... now it works.

After sitting on the bench for 5 hours, I plugged it in and it works.

The only explanation I can think of is this...

1. I soldered the pins to the board as usual...

2. I soaked the board in household ammonia to dissolve the flux...

3. Using compressed air, I dried the board, then immediately plugged it in for test.

Moisture from the ammonia bath must have screwed with the signals, after ammonia solution evaporation Teensy is happy again.

Unless anyone has a better explanation, I'm gonna call it solved.

Never experienced this problem before... but hey, LESSON LEARNED.


Yes, ammonium hydroxide (plus the non-pure water it's dissolved in) will conduct. Use isopropanol and a toothbrush to clean off flux.
Its a strong alkali. (NH4+/OH-), strong acids and bases have no place in electronics, they can permeate the PCB material and hang around for ages too, especially acids which liberate free protons that can diffuse through almost any material... This can lead to metal corrosion over time. They can also attack some plastics and weaken them.

Aqueous strong acids and bases are extremely good conductors of electricity since they are highly ionized, ions are charged particles...

Best to rinse with de-ionized water, then dry, then rinse with IPA, then dry again, hopefully no lasting effects.
Good to know, thanks.

When I make my own 1 side PC Boards, I spray orange paint on the non-trace side of the board.

I the image the paint ( which is very receptive to the wavelength of the blue laser on my CNC ), with the silkscreen file, allowing a simulated silk-screen parts placement image. ( see attached )

Problem is...IPA attacks the paint, hence the ammonia cleaner.

Guess I'm going to have to find a different flux cleaner that wont dissolve the paint.

Any suggestions appreciated.




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Thanks for the link.

Water soluble flux looks like the solution to my problem... didn't know there was such a thing.

I'll certainly give it a try.


Hello All,

I purchased the Kester2331zx-p Water Soluble Flux Pen and it works great.

Washes off, doesn't harm the paint.

Not only is it water soluble, it cleans better than what I was using ( CS-Flux )


I felt like a cave man who's discovered fire.

Thanks For the help.