Blown ATmega8U2

[countglockula]

This is a good test, for sure.

However, if the Arduino-computer can't establish a COM port, I think it's safe to say that either the software drivers are blown (computer issue), or the 8U2 has lost its magic smoke(Uno issue).

I let it out of mine earlier today when a stray connection between Vcc and the back of the board occurred.

So, assuming the 8U2 is gone, and I am able to replace it, then what about its internal firmware? How is that replaced? Or is it even replaceable?

Inquiring minds want to know if its worthwhile replacing the chip?

Cheers,
Ron

[Coding Badly]

So, assuming the 8U2 is gone, and I am able to replace it, then what about its internal firmware?

Like all things Arduino, the firmware is open source.  Everything you need (except an ISP) is in this directory...

[font=Courier New]  {ArduinoBaseDirectory}\hardware\arduino\firmwares[/font]

How is that replaced?

Connect an ISP (In System Programmer) to the six-pin connector closest to the ATmega8U2 then upload.

Or is it even replaceable?

Only you can answer that question.  Have you ever removed a surface-mount component from a PCB?

[CrossRoads]

That part has teeny, tiny pins!

[countglockula]

Thanks for the answers to my questions. After finding out what to look for, I began digging vigorously through the mound of available Arduino data. I was able to come up with the hex code for the 8U2 and instructions for using the second ISP connector. Armed with my trusty AVRisp Mk II I was able to access the 8U2, clear it out, and successfully upload the firmware.

Sadly, my poor Uno has an additional problem. The 'accident' fried a small trace leading from Vin to parts unknown. I replaced the run with some #30 insulated solid wire, and was again good to go. However, the board is drawing excessive current. I removed the ATMega328P, which dropped current by 10ma. Still pulling about 120ma, when it should be around 30 - 40ma.

The voltage regulators are seemingly good, each supplying its appropriate voltage  ... 5 and 3.3 respectively. So I still have something blown somewhere and need to find it.

PostScript:
It does appear that the 8U2 is partially smoked. It has lost some of its code and now will NOT reprogram. I have ordered a few of these from Mouser and will attempt a repair. I'll be using ChipQuik to remove the chip (awesome product - everyone needs one of their removal kits) and will then use hot air to replace it.
As an aside, I made a very good hot air rework tool using a Paladin hot-air gun and a couple of reworked metal funnels to make concentrators. A $50 investment that has paid for itself many times over.
I'll let everyone know how this comes out. I hate throwing out good stuff just because it has a little boo-boo.

Cheers, and thanks again for putting me on the right track!

Ron