Arduino mega 2650 usb problem?

We have encoutered a problem with our new arduino mega 2650 board. After a week it stopped recogniting the board as a usb/com port. We where powering the board with a external ac/dc 12v adaptor. There was a h-bridge(devantech md22) and a rs232/ttl converter connected to the board. Both where powered trough the on-board power regulators.

The board itself is still working, and we are able to program it trough pin 0 and 1 with the ttl converter. When connected with the usb plug it does start up and runs as normal, but programming trough usb is impossible. Also the tx and rx leds doesn’t light up once. There is no device visible in the device manager when plugged in.

Hope you guys can help…

If you upload a sketch that transmits serial data, can you receive it via the USB connection to the board? You could try reflashing the firmware onto the 8U2 on the Mega 2560 that serves as the USB-serial bridge.

No, if we send serial data we can receive it trough pin 0 and 1. Not via the USB connection. Also the leds doesn't light up. How do you reflash the firmware on the Mega 8U2? And does that dispose my chance on factory waranty?

Btw: I have access to a stk 500 and another arduino if necessary...

Here are some instructions for reflashing the 8U2 firmware: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1286088093/34#34

Ok, but if i understand correct that is to reflash the 8U2 via the usb port. But the problem is that the pc doesn't recognize the 2650 at all. It does not show up in the device manager. Is it possible to reflash the complete 8U2 with the provided "MEGA-dfu_and_usbserial_combined.hex" file via the isp header with a stk 500?

I have had the exact same problem. Would love to hear any potential solutions. I plugged in an UNO I had and Windows 7 immediately recognized it, so it's not a driver issue.

I also have a mega 2560 with the exact same problem. USB stopped working after a week. I was able to re-flash the 16u2, but this didn’t fix it. Could it be bad solder on the 16u2?

I'm starting to see this allot on various forums, but have not heard of any successes yet. I'm unsure if my mega shipped with the old usb converter firmware that would need an update. Could this problem be a symptom of the old firmware?

So now the same thing for me. I have a modified program uploaded to the Mega2650 that runs as soon as I power up. If I compile any other sketch, it compiles cleanly and says it has uploaded to the Mega, but the TX/RX lights don't flash anymore to signal uploading of program data and the old program is still running.

The serial data back thru the USB is working because my Serial.println is still showing up in the Serial monitor

It doesn't seem like reflashing is the answer. What else can this be ? Kind of a useless piece of hardware if you can't use it after a week or so :~

I know this is an old thread, but Mega USB has just packed up for no reason.

It’s still running the application code, but it’s not detected as a serial port any more.

Did anyone find a reason for this?

I guess I can still use the ISP header or hang a TTL serial USB dongle off the Tx Rx pins…