I can only flash my Uno via ICSP, not USB/Serial (ttyACM0)

I may have fried something on my Uno. I have 2 Unos. One, I can flash just fine from arduino. The other one, also shows up as ttyACM0, but flashing gives me the stk500 not responding error.

If I use the ICSP header, I can reflash the Uno and then it works fine. I tried to reflash the 16U2 (my Uno r3 is the one that won't flash via USB/Serial), the procedure with dfu works fine, ttyACM0 goes away, then comes back, everything looks good. And then I plug it back into the arduino IDE, and it won't flash. If I plug my other Uno without changing anything, again that one flashes fine.

What are possible failure scenario there?

Are you saying you've programmed the '328p on your Uno r3 via ICSP? (ie, by doing 'upload using programmer')

If you do that, it erases the serial bootloader; you need to connect it to the ICSP programmer and do 'burn bootloader' if you want to again upload sketches via serial again.

I may have fried something on my Uno.
I have 2 Unos. One, I can flash just fine from arduino.
The other one, also shows up as ttyACM0, but flashing gives me the stk500 not responding error.

If I use the ICSP header, I can reflash the Uno and then it works fine.
I tried to reflash the 16U2 (my Uno r3 is the one that won’t flash via USB/Serial), the procedure with dfu works fine, ttyACM0 goes away, then comes back, everything looks good.
And then I plug it back into the arduino IDE, and it won’t flash via USB, but it’ll flash via ICSP. If I plug my other Uno without changing anything, again that one flashes fine via USB.

What are possible failure scenario there?

DON'T CROSS POST!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! http://forum.arduino.cc/index.php?topic=467864 Reported

Threads merged.

DrAzzy: Are you saying you've programmed the '328p on your Uno r3 via ICSP? (ie, by doing 'upload using programmer')

If you do that, it erases the serial bootloader; you need to connect it to the ICSP programmer and do 'burn bootloader' if you want to again upload sketches via serial again.

Aaah, that would explain why I had the problem then, I didn't realize uploading via ICSP also deleted the bootloader. I re-burned a bootloader, and things are ok again.

And sorry about the crosspost, I couldn't figure out which of those 2 places was best for this message.

Thanks for your help.