Probably....best I can do...Give it a shot and tell us what happens!

You can just remove that transistor that connects usb to the 5v rail - easy mod, takes 30 seconds, seems to work fine. After the mod you MUST supply power via the 5v bus, usb power won't work after that.

Hi David,

Thank you, unfortunately the changes to the mega2560 zip file haven't taken effect yet (from hawaii), here's the link that the web site gives me:

http://arduino.cc/en/uploads/Main/arduino-mega2560_R3-reference-design.zip

Thanks for working on this, I'll try again later.

Mahalo,
Kurt

Maybe some of my bricked Megas can load sketches from their ICSP ports.

In my case, the mega's with dead usb ports could still have sketches uploaded via the ICSP.

David,

I want to thank you and the entire Arduino team for standing by your products. The offer to replace the boards is very much appreciated as each and every board we purchased was intended to go into the first actual customer installations of a new product. Getting to this point has been very expensive for the new co. that designed and built the first prototypes of the new product. Even though the Arduino's were among the less expensive of the components involved every little bit helps, and the replacement boards should hopefully end up in the hands of actual customers (buried inside little black boxes!).

Your reply, and the honesty within is very much appreciated, and we will do all we can spread the word that Arduino and the people behind it are a good investment.

Now then, (and grinning) - while you're changing the mega2560 documentation on the web site could you please get somebody to fix that broken zip file containing the reference design for the rev3?

Thanks,
Kurt Olsen

(Now... what to do with these bricked Megas?)

I think they should be sent back to the vendor with a warranty replacement request. The vendors get away with a lot that wouldn't be tolerated in consumer products under the umbrella 'electronic hobbyists'. And in this case I think that replacements are justified. I hope to do this as soon as I have a talk with my customer, who purchased the boards I used in development. My usage of the boards falls within all the documented specifications, and there are no caveats mentioned about usb and external power. If distributors start getting boards back then that drives change at the manufacturing level.

Note that I've sent emails to both sales and team at arduino.cc asking them to look at this problem AND to fix the broken zip file containing the rev3 reference design. First I emailed sales, then a week later forwared to team, after 10 days or so I still haven't received a reply and the broken zip file is still un-openable....nobody's home....

Hi Eraticus, also note that holding down the shift key while clicking the upload icon (not the menubar) will command an 'upload with programmer' - I don't think upload.using is being used (or is not working) anymore.

We should know in a couple of days if the particular board I removed T2 from dies. But this won't be a very definitive test in that I'm sticking with this one particular mega, running on external power from an OKI-78 dc-dc converter. If it dies, then the OKI-78 is probably doing it or, it's a bad batch of 16u2's....I'd suggest just starting your project on a board with T2 removed to be on the safe side.

The following instructions can be used to restore the 16u2 firmware on an arduino mega2560, rev 3. Using a Macintosh/osX (Lion), with the Arduino IDE 1.0.0 installed in the applications folder.

1) Plugin a usb cable to the arduino mega rev3 in order to supply it with power.

2) Plugin an avrispmkII programmer into the 6 pin icsp1 jack located adjacent to the usb connector (observe pin1 orientation via the dot on the board). I had to use an 'extender' for the icsp1 connector as the avrispmkii connector wouldn't fit due to proximity to one of the edge-connectors on the arduino.

3) Open a terminal window, paste in the following command and execute it:

/Applications/Arduino.app/Contents/Resources/Java/hardware/tools/avr/bin/avrdude -C /Applications/Arduino.app/Contents/Resources/Java/hardware/tools/avr/etc/avrdude.conf -p m16u2 -F -P usb -c avrispmkii -U flash:w:/Applications/Arduino.app/Contents/Resources/Java/hardware/arduino/firmwares/Arduino-COMBINED-dfu-usbserial-atmega16u2-Mega2560-Rev3.hex  -U lfuse:w:0xFF:m -U hfuse:w:0xD9:m -U efuse:w:0xF4:m -U lock:w:0x0F:m

4) Unplug both the programmer and the usb cable, then plug the usb cable in and the mac (and the pc) should recognize the usb port.

I'd say the boards died within a 2-3 day time frame. I can't pin it down any closer than that because the usb cable was only plugged in intermittently but if I had to guess I'd say they had maybe 4-5 hours of time plugged into both usb and external power.

I'm not sure it's the culprit, but removing it prevents using both power supplies simultaneously while allowing usb communications. What do you think T2 might be doing to damage the 16u2?

Regarding my suspicion that simultaneously providing both usb power and external power to a mega2560 can damage the 16u2 (usb controller chip) I am now removing transistor T2 from the mega2560. This transistor is what allows usb power to be connected to the 5vdc bus. Removing it totally prevents usb power from being used.

Note that you cannot just clip the 5vdc wire (or an unpowered hub I think) because the usb power is applied to the 16u2 and is used to power an internal component which is used to provide power to the data lines. I tried this first, and it resulted in very very shaky usb connections. Sometimes it would connect, most times it wouldn't.

But removing T2 removes usb power from the 5vdc bus AND yet still allows usb communications to work properly.

to be continued...

I just retried the 16u2 firmware reloads on two of the arduino mega rev 3's - one reports the burn was ok, one reports verification errors, and neither can be recognized. I don't think there's anything left to try....

I'm confused too! - But I'll retry the one that didn't have verify errors just to make sure, I'll report back on that. Thanks.