Overvoltage damage.

I powered a Ladyaya Motor shield with 30V to drive a stepper,even though the power jumper was off one of the L293D's toasted.

On my Uno the center leg of the voltage regulator vaporized! Will I have taken out the USB chip as well?

If you plug it into your computer you should find out. Try uploading a program and see if it works. If it doesn't, get a 5v regulator, set it up on a breadboard (don't forget capacitors) and connect the output directly to the 5v pin (WARNING: DO NOT PUT ANY VOLTAGE OTHER THAN 5v INTO THE 5v PORT AS IT CONNECTS TO THE VCC OF THE MICROCONTROLLER). If the board lights up and acts as usual, you may have fried the mega16u which means you have to program your board through the tx and rx pins. If neither works you have fried your board and/or your avr. If you really want to you can set up your avr standalone and see if it works.
If my memory is correct, the center leg is the ground which may be a bad sign.

-Luke

Thanks for that. I was a bit apprehensive connecting it incase I took out the USB port in my computer. It lights up, but AVRdude reports that it cant communicate. So I guess the mega16u is toast. I have another UNO so I think I'm going to check the ATMega in that.

Thanks for your help.

thebob:
but AVRdude reports that it cant communicate. So I guess the mega16u is toast.

If the board appears as a com port on your computer, that would indicate the 16u2 is fine.

If avrdude is giving you "out of sync" errors (on the correct serial port), then that would indicate the 328p needs to be replaced.

I would be cautious using the board anyway. If something failed short due to the high voltage, you may cause be drawing excessive current from USB or when other things are connected. Also, just because a component is damaged doesn't mean it fails right away. So if you ever have problems with the board in the future, it is probably related to the damage you did now.

The good news is that during the "incident" the port switched to a bluetooth port! Selecting the serial port again and I can upload a sketch, and everything seems to work fine... except of course the power port.

Now this is peculiar searching for a replacement 269-5G it appears that the regulator didn't have a middle leg!

I'm at a loss what to do. Is it OK to solder bridge the "stump" to the pad on the board.

The middle leg is the ground and so is the pad on the top. All three of my uno's have the middle leg soldered which means that yours being vaporized cannot be good. I advise against soldering it back to the pad because there is a small chance that the inside is toast, which could make a short between the input and output meaning that the 9v that you would put into the board will not be regulated and go straight into the avr.

-Luke