USB Serial

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I'm running arduino on Windows with a Teensy 3.5, and having a problem with Serial over USB on one of my Teensy 3.5 (the other Teensy 3.5 works fine with same USB cable, etc). The serial port does not show up in the Arduino GUI. I can program it, I just have to push the program button every time. And I can't get the Serial port to work at all, with the Arduino GUI or any other Serial terminal program (again, my other Teensy works just fine). Is there something I need to do to reset the serial port on this Teensy, or is it just dead? Funny that it programs though. Any suggestions?
 
Programming the Teensy is not done via Serial (as on Arduino for example) but via the HID protocol. The serial port will only show up when you load a sketch which has explicitly been compiled with one of the USB serial options. There are use cases like for example USB midi devices, where the presence of an USB serial port is neither desired nor needed.
 
Please re-read my post more carefully. You have described my problem exactly; the serial port does NOT show up when I load a sketch which has explicitly been compiled with one of the USB serial options. Also, the Teensy does not auto program from the Arduino IDE (I have to press the program button on the Teensy every time). My other Teensy do work as expected with the exact same sketches, etc (I am using the arduino example Serial Communications sketches).
 
Thanks, that does seem to be a similar problem to mine.

Although, I'm not sure if this has always been a problem with this particular Teensy. It doesn't make sense to me that I would have to reinstall the Windows Serial Installer as you described the fix for your problem because my other Teensies work just fine, but it seems worth a try, and I will do so when I get a chance. It's just that I've been using Teensies successfully for years without a problem, and now I have a problem with just one particular Teensy. Just weird that I CAN program it over USB, but I CAN'T get serial over USB to work.
 
Given the sometimes-flakey behavior of Windows driver installations, I’m more inclined to be happy that I found a solution rather than obsess over why it worked.
 
Yes, I understand that programming is over HID, but it seems to be a related USB issue to my USB serial problem, as programming over USB HID also has problems with this Teesny -- it does not automatically program without pushing the button on the Teensy. I'm just trying to point out that there is something strange going on with the USB port on this Teensy.
 
Have you tried that problematic board on other computers? Ideally you might trying Linux or a Mac, if you have access to any such machines. That might help you to know whether the problem is on the Teensy side or the Windows side.

Microsoft loves that Windows Registry. Even though the USB enumeration process involves reading all the USB descriptor info needed to fully identify the device, Windows *still* uses the stored into from its Registry in many cases. So if something got messed up with the Windows Registry, it's possible that stale/wrong info could be affecting that one board.
 
SOLVED!

Thanks for the help! It was that particular Windows box. The problem Teensy worked just fine on Linux and on another Windows box, but won't work on the original Windows box, even after a reboot. I think that I will need to go into the registry and clean out some USB/COM ports.
 
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