Uno no longer appears when plugged into USB WinXP

Hello, My UNO has been working fine for the past month, but today when I plugged in the USB connector, it no longer appears. I'm using a USB debugger (USBDeview) and it doesn't show up anymore.

Is there a way to do a hard reset on the board? The green light power light is active. Just can't tell if I hosed the board or have a bad sketch or something.

I googled here and only saw a few similar issues with no luck. Thx, pjt

Just can't tell if I hosed the board or have a bad sketch or something.

If it was a bad sketch it wouldn't stop it showing up as a USB device from the computer. It sounds like the USB / serial chip is not working properly. It is a very small surface mount part that is actually a programmable computer in it's own right. You can check if there is a clock signal from the crystal or resonator on a scope. Otherwise you need a new board.

Clock = yes

Any other debug steps you can think of between "valid clock" and "board is toast"? :-)

Thanks for the reply.

Peter

I have the same kind of problem, only i just shorted the board with 5V.

If the program is still running but your board just won't appear then i guess your MEGA8U2 is dead.

Don't know if you have any other boards lying around but you could test the chip on another one.

Any other debug steps you can think of between "valid clock" and "board is toast"

Well to be honest thee is not a lot because it is just an embedded processor. If it is receiving a clock, power and the reset is OK it can only be the software or toast. One thing you could do is to try and reprogram the MEGA8U2, the programmer would tell you if it is responding. However you do need programming hardware to do this.

Found the problem:

I removed the standoffs and the board went back to functioning properly.

This is weird because it has been on standoffs since the day I took it out of the box, and hadn't had any problems, so it wasn't on my list of things to debug.

However, I was using 1/4" metal hex standoffs, and I guess one of them turned and touched something it shouldn't have (although I don't see anything on the board that would be problematic).

Removing them solved the problem. (Nylon round ordered, btw.)

At least I know about the MEGA8U2 now.

Thanks for the help.

P

Thanks for reporting that back and adding it to the data base of what can go wrong, it's a new one on me. :)