New Arduino Uno R3 re-set problem.

My friend brought his brand new Uno R3 ( bought last saturday from one of the largest official stockists) for me to test. Loading any sketch produce the same results, connected to usb or external supply.
Symptoms are:-

  1. While connected to computer USB, load sketch, say “blink example” It appears to load ok with the leds flashing during data transmission, program runs ok with on-board LED flashing as it should.
  2. Press the reset button, program stops and does not restart until program is re-loaded. Disconnecting usb and reconnecting has the same effect as pushing the re-set button. It is the same if the re-set pin is used. I checked the re-set switch and it is mechanically and electrically fine.
  3. Do the same test but with a nine volt battery connected to the power input socket, load the sketch, remove the usb and the re-set button works once (program stops and re-starts) and then freezes again until the sketch is reloaded.
  4. Doing exactly the same, on the same computer with two of my boards and the re-set works properly every time.
    It would appear that the board is faulty, but a second/third… opinion would be appreciated in case we are missing something. :expressionless:


How exactly can you do that? I've having a similar problem with an Arduino Uno and I have an Arduino Mega .


Update to original post.
Today the board stopped working altogether so it was returned and replaced with a new one which is performing correctly.
It's a pity we never found out exactly what was wrong for future reference.